Drug companion protocol
Retatrutide
A triple receptor agonist (GLP-1, GIP, glucagon) in late-stage clinical development for obesity and metabolic disease.
Quickstart Highlights
- Drug class
- GLP-1 / GIP / glucagon triple receptor agonist
- Route
- Subcutaneous injection
- Schedule
- Once-weekly subcutaneous injection, titrated over 12–26 weeks from a starting dose of 2 mg/week
- Evidence score
- 55
Quickstart highlights
- 💉Subcutaneous injection
- 🔬GLP-1 / GIP / glucagon triple receptor agonist
- 🧪Lyophilised powder — requires reconstitution with bacteriostatic water
- 📋Prescription required
How this works
Mechanism of action and pharmacokinetic profile from published data.
Retatrutide is a novel triple receptor agonist that activates the glucagon, GIP (glucose-dependent insulinotropic polypeptide), and GLP-1 (glucagon-like peptide-1) receptors with balanced potency. The glucagon component is thought to increase energy expenditure; GIP and GLP-1 agonism improves insulin secretion, slows gastric emptying, and reduces appetite. Phase 2 data suggest weight-loss effects that exceed those reported for single- or dual-receptor agonists, though longer-term safety and efficacy are still being studied in Phase 3 trials.
Half-life
6 days
Tmax
2 days
Duration of action
7 days
- Time to peak (Tmax)
- 24–72 hours after a subcutaneous injection.
- Clearance
- Catabolised to small peptides and amino acids via proteolytic degradation; not primarily renally or hepatically cleared as intact drug.
- Elimination half-life
- Approximately 6 days in humans, which supports once-weekly subcutaneous dosing.
- Bioavailability
- High systemic exposure after subcutaneous injection; retatrutide is a peptide and is not orally bioavailable.
Dosing & Reconstitution Guide
Full preparation, protocol, and administration reference for compounded lyophilised formulations.
Dosage chart
Retatrutide — 5 mg vial
Retatrutide is dosed at 2 mg–8 mg weekly by subcutaneous injection in educational protocols, starting low and titrating monthly. A 5 mg vial reconstituted with bacteriostatic water yields about 5.0 mg/mL. This information is for research and educational use only.
- Reconstitute: Add 1.0 mL bacteriostatic water → ~5.0 mg/mL concentration.
- Typical weekly range: 2–8 mg once weekly (gradual escalation over 8–12 weeks).
- Easy measuring: At 5.0 mg/mL, 1 unit = 0.01 mL ≈ 50 mcg on a U-100 insulin syringe.
- Storage: Lyophilized: freeze at −20 °C (−4 °F); after reconstitution, refrigerate at 2–8 °C (35.6–46.4 °F) for up to 4 weeks.
Protocol overview
Once-weekly subcutaneous injection, titrated over 12–26 weeks from a starting dose of 2 mg/week. Most compounding pharmacies dispense 10 mg or 20 mg lyophilised vials; both yield a 10 mg/mL solution when reconstituted per the guide below. Dose escalation follows a prescriber-led schedule — the Phase 2 trial used 4-week intervals before each increase. The 12 mg/week arm produced a mean 24.2 % body-weight reduction at 48 weeks in the primary obesity trial.
Dose escalation phases
Advanced retatrutide Phase 2 high-dose reference
| Phase | Dose | Frequency | Guidance |
|---|---|---|---|
| Weeks 1-4 Week 1-4 | 2 mg | once weekly | Trial initiation and tolerability phase. Investigational schedule; follow prescriber or trial protocol. |
| Weeks 5-8 Week 5-8 | 4 mg | once weekly | First escalation step. Do not accelerate without protocol guidance. |
| Weeks 9-12 Week 9-12 | 8 mg | once weekly | Higher-dose escalation step. Monitor GI tolerability closely. |
| Week 13 onward Week 13+ | 12 mg | once weekly | Highest Phase 2 reference dose. Investigational; not an approved maintenance dose. |
Standard retatrutide Phase 2 reference
| Phase | Dose | Frequency | Guidance |
|---|---|---|---|
| Weeks 1-4 Week 1-4 | 2 mg | once weekly | Trial initiation and tolerability phase. Investigational schedule; follow prescriber or trial protocol. |
| Weeks 5-8 Week 5-8 | 4 mg | once weekly | First escalation step. Hold or adjust only under protocol guidance. |
| Weeks 9-12 Week 9-12 | 6 mg | once weekly | Intermediate escalation step. Do not self-escalate. |
| Week 13 onward Week 13+ | 8 mg | once weekly | Higher-dose trial reference. Investigational; not an approved maintenance dose. |
Supplies needed
- ◦Prescribed retatrutide lyophilised vials — Your compounding pharmacy will dispense the vial size and quantity prescribed. Check the label matches your prescription.
- ◦Bacteriostatic water for injection (10 mL vials) — Bacteriostatic water (BAC water, 0.9% benzyl alcohol) is used as the reconstitution diluent. Sterile water for injection is an alternative but offers no bacteriostatic protection; use reconstituted solution within 24 hours if sterile water is used.
- ◦U-100 insulin syringes (1 mL) — Use 1 mL U-100 syringes — they are calibrated in 1-unit increments (1 unit = 0.01 mL). Common needle sizes: 29G–31G × 5–8 mm. Use one syringe per injection; never reuse.
- ◦Alcohol swabs — To wipe the vial rubber stopper and injection site before each use.
- ◦Labels and a fine-tip marker — Label each vial with the reconstitution date and concentration so you can track the 4-week use window.
- ◦Sharps disposal container — A rigid, puncture-resistant container for used syringes and vial caps.
5 mg vial — dosing tables
Standard / Gradual Approach
Conservative titration for the 5 mg vial reconstituted with 1.0 mL bacteriostatic water (~5.0 mg/mL).
| Phase / Dose | U-100 Units | Volume (mL) |
|---|---|---|
| Weeks 1–4 | 40 | 0.40 |
| Weeks 5–8 | 80 | 0.80 |
| Weeks 9–12 | 120 | 1.20 |
| Weeks 13+ | 160 | 1.60 |
Advanced / Aggressive Protocol
Higher-dose escalation for the 5 mg vial at ~5.0 mg/mL. Doses above 5 mg require multiple vials.
| Phase / Dose | U-100 Units | Volume (mL) |
|---|---|---|
| Weeks 1–4 | 40 | 0.40 |
| Weeks 5–8 | 80 | 0.80 |
| Weeks 9–12 | 160 | 1.60 |
| Weeks 13+ | 240 | 2.40 |
10 mg vial — dosing tables
Standard / Gradual Approach
Conservative titration for the 10 mg vial reconstituted with 1.0 mL bacteriostatic water (~10.0 mg/mL).
| Phase / Dose | U-100 Units | Volume (mL) |
|---|---|---|
| Weeks 1–4 | 20 | 0.20 |
| Weeks 5–8 | 40 | 0.40 |
| Weeks 9–12 | 60 | 0.60 |
| Weeks 13+ | 80 | 0.80 |
Advanced / Aggressive Protocol
Higher-dose escalation for the 10 mg vial at ~10.0 mg/mL. The 12 mg dose requires two vials.
| Phase / Dose | U-100 Units | Volume (mL) |
|---|---|---|
| Weeks 1–4 | 20 | 0.20 |
| Weeks 5–8 | 40 | 0.40 |
| Weeks 9–12 | 80 | 0.80 |
| Weeks 13+ | 120 | 1.20 |
20 mg vial — dosing tables
Standard / Gradual Approach
Conservative titration for the 20 mg vial reconstituted with 2.0 mL bacteriostatic water (~10.0 mg/mL).
| Phase / Dose | U-100 Units | Volume (mL) |
|---|---|---|
| Weeks 1–4 | 20 | 0.20 |
| Weeks 5–8 | 40 | 0.40 |
| Weeks 9–12 | 60 | 0.60 |
| Weeks 13+ | 80 | 0.80 |
Advanced / Aggressive Protocol
Higher-dose escalation for the 20 mg vial at ~10.0 mg/mL. All doses up to 12 mg fit in one reconstituted vial.
| Phase / Dose | U-100 Units | Volume (mL) |
|---|---|---|
| Weeks 1–4 | 20 | 0.20 |
| Weeks 5–8 | 40 | 0.40 |
| Weeks 9–12 | 80 | 0.80 |
| Weeks 13+ | 120 | 1.20 |
30 mg vial — dosing tables
Standard / Gradual Approach
Conservative titration for the 30 mg vial reconstituted with 3.0 mL bacteriostatic water (~10.0 mg/mL).
| Phase / Dose | U-100 Units | Volume (mL) |
|---|---|---|
| Weeks 1–4 | 20 | 0.20 |
| Weeks 5–8 | 40 | 0.40 |
| Weeks 9–12 | 60 | 0.60 |
| Weeks 13+ | 80 | 0.80 |
Advanced / Aggressive Protocol
Higher-dose escalation for the 30 mg vial at ~10.0 mg/mL. Efficient for complete protocols from a single vial.
| Phase / Dose | U-100 Units | Volume (mL) |
|---|---|---|
| Weeks 1–4 | 20 | 0.20 |
| Weeks 5–8 | 40 | 0.40 |
| Weeks 9–12 | 80 | 0.80 |
| Weeks 13+ | 120 | 1.20 |
Reconstitution steps
Vial size
5 mg
BAC water to add
1 mL
Resulting concentration
5 mg/mL
At 5.0 mg/mL, 1 U-100 unit = 0.01 mL = 0.05 mg (50 mcg).
Draw 1.0 mL bacteriostatic water with a sterile syringe. Inject slowly down the vial wall; avoid foaming. Gently swirl or roll until dissolved (do not shake). Label with date and refrigerate at 2–8 °C (35.6–46.4 °F), protected from light.
Vial size
10 mg
BAC water to add
1 mL
Resulting concentration
10 mg/mL
At 10 mg/mL: on a U-100 insulin syringe, 1 unit = 0.01 mL = 0.1 mg of retatrutide.
Allow the vial to reach room temperature before opening — this reduces condensation inside the vial. Remove the protective cap from the vial. Wipe the rubber stopper with an alcohol swab and allow to dry. Draw 1.0 mL of bacteriostatic water into an insulin syringe. Insert the needle through the rubber stopper and inject the water slowly down the inner wall of the vial — do not squirt it directly onto the powder. Gently swirl or roll the vial between your palms until the powder is fully dissolved. Do not shake — shaking can degrade the peptide. Hold the vial up to the light and inspect: the solution should be clear and colourless. A very faint yellow tinge is sometimes normal for retatrutide but discard if cloudy, visibly particulate, or strongly discoloured. Label the vial with the reconstitution date and concentration (10 mg/mL). Refrigerate immediately.
Vial size
20 mg
BAC water to add
2 mL
Resulting concentration
10 mg/mL
At 10 mg/mL: on a U-100 insulin syringe, 1 unit = 0.01 mL = 0.1 mg of retatrutide.
Allow the vial to reach room temperature before opening. Wipe the rubber stopper with an alcohol swab and allow to dry. Draw 2.0 mL of bacteriostatic water. Inject slowly down the inner vial wall — do not squirt directly onto the powder. Gently swirl or roll until fully dissolved. Do not shake. Inspect: solution should be clear and colourless. Discard if cloudy or particulate. Label with reconstitution date and concentration (10 mg/mL). Refrigerate immediately. For extended storage: the reconstituted solution may be aliquoted into smaller volumes using sterile technique and frozen at −20 °C. Thaw each aliquot once only — do not refreeze.
Vial size
30 mg
BAC water to add
3 mL
Resulting concentration
10 mg/mL
At 10.0 mg/mL, 1 U-100 unit = 0.01 mL = 0.1 mg (100 mcg).
Draw 3.0 mL bacteriostatic water with a sterile syringe. Inject slowly down the vial wall; avoid foaming. Gently swirl or roll until dissolved (do not shake). Label with date and refrigerate at 2–8 °C (35.6–46.4 °F), protected from light.
Injection steps
- 1Wash your hands thoroughly
- 2Set up a clean workspace
Use a clean, flat surface. Lay out your supplies. Do not work near an open window or fan.
- 3Draw up your dose
Wipe the vial rubber stopper with a fresh alcohol swab. Allow to dry. Draw back the syringe plunger to your target volume to fill with air, then inject air into the vial (inverted) before drawing the solution — this makes extraction easier. Pull back the plunger to draw the exact volume for your prescribed dose. Refer to the concentration reference table above for the mL volume for your dose.
- 4Remove air bubbles
Hold the syringe needle-up, tap to bring bubbles to the top, and gently press the plunger to expel air. Recheck that the volume is correct.
- 5Choose and clean your injection site
Rotate between the abdomen (at least 5 cm from the navel), front of the upper thigh, and upper arm. Wipe with an alcohol swab and allow to dry completely before injecting.
- 6Inject subcutaneously
Pinch a skinfold if you have a thin subcutaneous layer. Insert the needle at 45–90° into the fatty tissue. Do not aspirate for subcutaneous injections. Inject slowly and steadily. Wait 3–5 seconds before withdrawing.
- 7Withdraw and apply gentle pressure
Withdraw the needle smoothly. Apply light pressure with a clean swab — do not rub. A small bleed or bruise is normal.
- 8For doses above 1.0 mL, split the injection
Volumes greater than 1.0 mL should be split across two injection sites at different locations to reduce discomfort and local absorption issues.
- 9Dispose and return vial to fridge
Place the used syringe directly into your sharps container. Return the reconstituted vial to the refrigerator (2–8 °C). Record the injection date, site, and dose.
Storage instructions
Before reconstitution
Store lyophilized vials at −20 °C (−4 °F) or colder. Allow to reach room temperature before reconstituting.
After reconstitution
Refrigerate at 2–8 °C (35.6–46.4 °F). Protect from light.
Use within 4 weeks of reconstitution.
Important notes
- !Your prescriber determines your dose and escalation — not this guide
The dose reference tables on this page are drawn from published Phase 2 trial protocols. Your actual prescribed dose, escalation schedule, and target may differ. Always follow your prescriber's instructions.
- !Never inject into a vein or muscle
Retatrutide is a subcutaneous injection only. Intravenous or intramuscular injection changes absorption kinetics and can cause serious reactions.
- !Rotate injection sites every week
Injecting the same spot repeatedly causes lipohypertrophy — a hardened lump that impairs absorption unpredictably.
- !Do not shake the reconstituted vial
Shaking can cause foaming and peptide degradation. Swirl or roll gently only.
- !Discard reconstituted vial after 4 weeks
Even refrigerated, reconstituted peptide degrades over time and bacteriostatic protection is not indefinite. Label every vial with the reconstitution date.
- !Do not use if solution is cloudy or has particles
These are signs of degradation or contamination. Discard the vial and contact your pharmacy.
- !Compounded retatrutide is not TGA-approved
Retatrutide has not been approved by the TGA, FDA, or EMA. Compounded versions dispensed by Australian compounding pharmacies operate under different regulatory pathways. Discuss this with your prescriber.
- !Tell all healthcare providers you are using retatrutide
Slowed gastric emptying affects fasting preparation for procedures and absorption of other oral medicines.
Sharps disposal
- ◦Place all used syringes in a sharps container immediately after use — Do not recap needles with two hands — use the one-hand scoop technique if recapping is necessary.
- ◦NestSafe sharps mail-back program (Australia) — Free household sharps mail-back. Collect a kit from participating pharmacies or via nestsafe.com.au.
- ◦EnviroSafe sharps mail-back (Australia) — Available from participating pharmacies at no cost to patients.
- ◦Community pharmacy drop-off — Many Australian pharmacies accept full sharps containers. Ask your dispensing pharmacy.
- ◦Vial disposal — Empty glass vials can be placed in a sharps container or returned to your compounding pharmacy if they offer a take-back service.
Concentration calculations are standard compounding arithmetic. Protocol phases are drawn from published Phase 2 trial data. Your prescriber and dispensing pharmacy determine the actual dose, vial size, and escalation schedule for your treatment.
Your journey
Where you are in a typical protocol, and what one dose cycle looks like. Educational — your prescriber tailors the plan to you.
Protocol timeline
Maintenance phase — prescriber-defined dose
Weeks 25+every 7dWhat to expect: Weight change typically plateaus as the body reaches a new set point, Appetite effects are sustained while on medication, GI side effects usually settle substantially in maintenance, Long-term safety data are still being collected in ongoing Phase 3 trials
Focus on: Maintaining healthy eating habits and physical activity to support outcomes, Continuing regular check-ins with your prescriber, Reporting any new or changing symptoms promptly, Discussing the long-term plan with your prescriber — retatrutide remains investigational
Common adjustments: Dose may be adjusted up or down depending on tolerability and goals, at prescriber discretion, Ongoing monitoring of any metabolic markers as directed by your prescriber
Starter phase — 2 mg/week
Weeks 1–42 mgevery 7dWhat to expect: Body is beginning to adjust to the medication — changes may be subtle at this stage, Mild reduction in appetite may begin to appear, Nausea and GI upset are most likely to occur during the first few weeks as your body adapts, Injection-site reactions (redness, mild swelling) are possible
Focus on: Establishing a consistent injection day and time each week, Learning correct reconstitution technique (lyophilised vial to 10 mg/mL solution), Recording side effects and appetite changes in your companion app or journal, Staying well hydrated
Common adjustments: Prescriber may extend this phase beyond 4 weeks if GI side effects are significant, Small, frequent meals are often recommended to manage nausea during this window
Escalation step 1 — 4 mg/week
Weeks 5–84 mgevery 7dWhat to expect: Appetite suppression typically becomes more noticeable, GI side effects (nausea, constipation, mild reflux) may increase transiently with dose increase, Some weight change may become measurable by the end of this phase, Energy expenditure may begin to increase due to glucagon receptor activation
Focus on: Monitoring and logging GI symptoms after each dose, Adjusting meal size — smaller portions more frequently, Maintaining protein intake despite reduced appetite, Noting any changes in bowel habit and reporting persistent constipation to your prescriber
Common adjustments: Prescriber may hold at 4 mg for longer if tolerability is a concern, Anti-nausea strategies (meal timing, food choices) become important this phase
Escalation step 2 — 6 mg/week
Weeks 9–126 mgevery 7dWhat to expect: Continued and often more pronounced appetite reduction, Progressive weight change expected to become clearly visible on the scales, GI symptoms may settle compared to the previous escalation step, Some people notice improved energy levels as weight changes accumulate
Focus on: Prioritising nutrient-dense foods — protein, vegetables, and wholegrains — despite lower caloric intake, Continuing weekly weigh-ins at the same time of day, Staying alert to red-flag symptoms (see red-flag guidance), Discussing any changes in mood or energy with your prescriber
Common adjustments: Prescriber may adjust if glucose levels are being monitored and require attention, Dose may be held or reduced if GI symptoms remain unacceptable
Escalation step 3 — 8 mg/week
Weeks 13–168 mgevery 7dWhat to expect: Appetite suppression is typically well established by this phase, Caloric intake may be significantly reduced; nutritional quality becomes critical, Body weight reduction continues; rate may begin to plateau in some individuals, GI side effects often less severe than at earlier escalation steps
Focus on: Ensuring adequate daily protein (discuss target with your prescriber or dietitian), Monitoring for signs of muscle loss — discuss resistance activity with your healthcare team, Checking in with your prescriber about whether escalation to the next step is planned
Common adjustments: Prescriber may introduce higher doses (10–12 mg) based on response and tolerability, Blood glucose monitoring frequency may be discussed if clinically indicated
High-dose escalation — 10–12 mg/week
Weeks 17–2412 mgevery 7dWhat to expect: This dose range produced the most substantial weight changes in Phase 2 trial data (mean ~24.2% body-weight reduction at 48 weeks for the 12 mg arm), Appetite suppression is typically pronounced; intentional eating planning is important, GI side effects may transiently re-emerge with each step up, Glucagon-mediated energy expenditure effects are expected to be active at this range
Focus on: Working closely with your prescriber and/or dietitian on nutritional adequacy, Tracking weight, energy, and GI symptoms at every weekly check-in, Being aware that this is still an investigational phase — reporting all symptoms is important, Understanding that Phase 3 trial data are still being gathered; long-term outcomes are not yet fully characterised
Common adjustments: Prescriber will determine whether 10 mg or 12 mg is appropriate based on individual response, Some prescribers hold at 10 mg for extended periods before moving to 12 mg
One dose cycle at a glance
Population typicals, in hours from your dose — individual experience varies.
Onset
24 h
Peak effect
24–72 h
Appetite effect
24–168 h
Nausea risk
12–96 h
Constipation risk
24–168 h
Coverage fades after
168 h
Based on published Phase 2 pharmacokinetic data: tmax approximately 24–72 hours after subcutaneous injection; half-life approximately 6 days, supporting once-weekly dosing. Appetite suppression and GI effects typically track the rising and peak drug-concentration window. Coverage is designed to extend for the full 7-day (168 h) dosing interval. All windows are population-typical estimates — individual experience will vary. Retatrutide is investigational; these figures are derived from Phase 2 trial data only.
Clinical Benefits & Side Effects
Observed outcomes, adverse effects, and lifecycle considerations from published trial data.
Benefits
Starting treatment
Trials began at a low dose (typically 2 mg weekly subcutaneously) and escalated in steps over several weeks. Expect a prescriber-led titration schedule rather than starting at a target dose.
First injection — taking the first step
You've done it — your first injection is behind you. This week is about getting familiar with the process and listening to your body. You may feel completely normal, or you might notice mild nausea, a reduced appetite, or some fatigue — all of these are common early signs that the medication is working.
Body beginning to notice the change
Side effects like nausea, bloating, or a feeling of fullness after small meals may become a little more noticeable this week. These sensations are your body adjusting to retatrutide's effects on multiple gut and metabolic receptors. Try not to be discouraged — most people find these symptoms manageable with the right eating habits and hydration.
Finding your post-injection rhythm
By now you may be identifying patterns — perhaps nausea peaks a day or two after your injection and then settles. Use this knowledge to plan lighter meals and gentler activities around your injection day. Weight change at this stage is unlikely to be dramatic, and that's completely normal.
Completing your first month — well done
You've reached the end of your first month, and that is genuinely worth acknowledging. Your dose is still in its early phase, so visible results on the scale may be modest or not yet present — and that's okay. Focus on building consistent habits around food, hydration, and sleep this week rather than the number on the scales.
Early GI adjustment
Across Phase 2 trials, nausea, mild diarrhoea, or reduced appetite most often appeared in the first 4–8 weeks while the dose was escalating, then eased with continued use. Slow-paced eating and good hydration helped many participants.
Dose may increase — appetite shifts ahead
If your prescriber has scheduled a dose escalation, you may notice stronger appetite suppression over the coming days — follow your prescriber's instructions carefully regarding any dose changes. Some people experience a return of nausea as the dose adjusts upward; the strategies that helped in weeks 1–4 will serve you well again here.
Appetite suppression becoming more noticeable
Many people start to feel a meaningful reduction in hunger and food 'noise' — that constant background thinking about food — around this week. It can feel quite unfamiliar to feel satisfied with a smaller plate. Try to honour your body's new hunger signals without undereating to the point of dizziness or fatigue.
Side effects
Small average increases observed across dose arms
~15–20%
- Pause solid food briefly, sip fluids, and restart bland foods once settled; do not escalate dose while vomiting persists.Seek help: Seek urgent advice for repeated vomiting, dehydration, or inability to keep fluids down.
Reported; less frequent than some other GLP-1 family agents
- Rotate sites, let alcohol dry before injecting, and avoid bruised, scarred, or hardened skin.Seek help: Seek advice for spreading redness, warmth, pus, fever, or severe pain.
Frequently reported — often an intended effect of the medicine
~25–30%
- Prioritise fluids and electrolytes; avoid alcohol, greasy meals, and very high-sugar drinks until symptoms settle.Seek help: Seek help if diarrhoea is severe, bloody, accompanied by fever, or causes dehydration.
Reported; dose-related
Reported; dose-related
- Increase fluids, fibre-rich foods, and gentle movement; consider pharmacist advice for a short-term stool softener if needed.Seek help: Contact a clinician for severe abdominal pain, no bowel movement for several days, or vomiting with constipation.
~35–50% at 12 mg; most common during titration
- Eat smaller, slower meals; choose bland lower-fat foods during escalation; avoid lying down soon after eating.Seek help: Contact your prescriber if nausea is severe, persistent, or prevents eating and drinking.
Lifecycle factors
Keep a brief symptom log
A few lines per day covering nausea, appetite, bowel habits, and any dizziness gives your prescriber real information to titrate against. Trial participants who tracked symptoms had a better conversation at their next visit.
Manage nausea with the BRAT-style approach
On days when nausea is significant, reach for bland, easily digestible foods — plain crackers, dry toast, steamed rice, or a mild broth. Cold or room-temperature foods are often better tolerated than hot meals when your stomach is unsettled. Ginger tea or ginger chews are a practical, evidence-informed option worth keeping in the pantry. If nausea is severe or persistent, always let your prescriber know — don't just push through.
Early GI symptoms are usually transient
In Phase 2, most nausea and GI symptoms were mild to moderate and occurred during the first 4–8 weeks of titration. They generally improved with continued use — but if they are severe or persistent, contact your prescriber.
Weight may return after stopping
Retatrutide suppresses appetite by activating receptors that control hunger and energy expenditure — effects that subside once the drug clears. With a half-life of ~6 days, retatrutide takes roughly 5–6 half-lives (30–36 days) to be almost entirely eliminated. Without a transition plan, most people regain a portion of lost weight over the following months. Talk with your prescriber before stopping — some patients transition to a lower maintenance dose (2–4 mg/week) rather than stopping abruptly.
Allow enough time for meaningful results
Phase 2 trials ran for 36–48 weeks, and most participants reached their lowest weight between weeks 24 and 48. Starting a course with a short-term mindset (under 12 weeks) is unlikely to produce sustained results — the dose is still escalating during that window and weight loss typically accelerates after week 12.
Important note
This content is intended for therapeutic educational purposes only and does not constitute medical advice, diagnosis, or treatment. Retatrutide is not TGA/FDA-approved and is available only for research purposes. All information presented is based on published clinical trial data and is not intended to encourage off-label use.
Nutrition & practical guidance
Food, hydration, and adherence tips compiled from trial data and clinical companion content.
Food and hydration
✅ Prefer
⚠️ Limit
Adherence tips
Rotate your injection sites consistently
Retatrutide is given as a weekly subcutaneous injection into the abdomen, outer thigh, or upper arm — follow your prescriber's instructions on technique. Rotating your injection site each week (e.g. left abdomen → right abdomen → left thigh) helps prevent skin irritation, lumps, or hardening at the injection site. Keep a simple log or diagram to track where your last injection was. If you notice unusual redness, swelling, or pain at any site, let your prescriber know.
Let the pen reach room temperature before injecting
Injecting medication straight from the fridge can cause stinging and discomfort at the injection site. Take your pen or syringe out of the fridge 20–30 minutes before your scheduled injection time and leave it on a clean surface away from direct sunlight. Do not warm it in hot water or a microwave — room temperature is all that's needed. This simple step can make your weekly injection noticeably more comfortable.
Eat slowly and stop earlier than you think you need to
Slowed gastric emptying means your satiety signal arrives later. Putting down the fork every few bites and pausing gives your brain time to catch up — most participants who tolerate the medicine well found their portions shrank gradually rather than all at once.
Do not self-adjust your dose
Phase 2 trials used a prescriber-led titration. Skipping doses to ease side effects, or jumping ahead to a higher dose, both increased adverse events in the trial data. Talk with your prescriber before changing anything.
Pick a consistent injection day and stick to it
Choosing the same day each week — say, every Sunday morning — helps build the habit and makes it easier to plan around any side effects. Many people choose a day when they have a lighter schedule the following day, in case nausea is present. Set a phone reminder if it helps. Always follow your prescriber's instructions if your scheduled day needs to change.
Sip water steadily — don't gulp large amounts
Drinking a large glass of water quickly can trigger or worsen nausea, especially in the early weeks. Instead, aim to sip water consistently throughout the day — small amounts, often. A 600 mL bottle at your desk or on your bench is a great visual reminder. Herbal teas like ginger or peppermint count toward your daily intake and may also settle an uneasy stomach.
Pick a consistent injection day
A weekly medicine is easier to remember when it is tied to the same day each week. If you miss a dose, there are published rules for how long after the scheduled day you can still take it — your prescriber or trial site will provide them.
Eat protein first at every meal
With a reduced appetite, every bite needs to work hard for you. Make protein the first thing you reach for — a few bites of chicken, some cottage cheese, eggs, or legumes — before moving to other parts of the meal. This helps ensure you're hitting your protein targets even on low-appetite days. A general guide is aiming for around 1.2–1.6 g of protein per kilogram of your body weight daily, but speak with your prescriber or a dietitian for personalised guidance.
Prioritise protein intake during weight loss
Aiming for roughly 1.2–1.6 g of protein per kg of body weight daily helps preserve lean mass while you lose fat. If your appetite is small, protein-first plating (protein before carbs or vegetables) helps.
Eat small portions slowly — and stop when satisfied
Retatrutide slows how quickly food leaves your stomach, which means fullness can arrive faster and more intensely than you're used to. Serve yourself smaller portions than you think you need, eat slowly, and pause between bites. Stopping at 'satisfied' rather than 'full' will help you avoid uncomfortable nausea and bloating after meals. Using a smaller plate can be a surprisingly effective way to recalibrate portion size.
Start with short walks and build gradually
You don't need to join a gym or run 5 km to support your progress — a 15–20 minute walk after dinner is a genuinely meaningful starting point. Movement helps with digestion, mood, and maintaining muscle mass during weight loss. As your energy improves over the coming weeks, aim to increase duration or add a second walk per day. Apps like Google Maps can help you measure distances in kilometres if you'd like to track your walks.
Include resistance training to protect muscle
When the body loses weight, it can lose muscle alongside fat — resistance training (bodyweight exercises, resistance bands, or weights) helps minimise this. You don't need to be experienced; simple exercises like squats, wall push-ups, and step-ups are a great beginning. Aim for two sessions per week and build from there. If you're new to exercise, a single session with an exercise physiologist can set you up with a safe, personalised routine.
Prioritise 7–9 hours of quality sleep each night
Sleep plays a direct role in appetite regulation, energy, and metabolic health — poor sleep can increase hunger hormones and undermine your progress. Try to keep a consistent bedtime and wake-up time, even on weekends. Avoid screens for 30–60 minutes before bed and keep your bedroom cool and dark. If sleep has been a long-standing challenge, it's worth raising with your prescriber as part of your overall health plan.
Measure progress beyond the scales
The number on the scales tells only part of the story — and in the early weeks, it may not move much at all. Track other meaningful markers: how your clothes fit, your energy levels throughout the day, how far you can walk, your sleep quality, and how you feel about your food choices. Consider keeping a brief weekly journal — even three or four sentences — to capture these non-scale wins. Progress is rarely linear, and the full picture is worth seeing.
Be kind to yourself on the hard days
Some weeks will feel harder than others — nausea, fatigue, slow progress, or simply life getting in the way. These are normal parts of the journey, not signs of failure. Reaching out to a friend, a support community, or a health professional on tough days is a sign of strength, not weakness. Remember: you are doing something meaningful for your long-term health, and every week you show up counts.
Daily companion
Practical playbooks for managing symptoms, eating around side effects, tracking what matters, and reporting back to your clinician.
Symptom playbooks
Nausea
Minimal or no nausea
Nutrition: Continue eating regular balanced meals, Maintain adequate protein at each meal, Keep meal portions moderate — avoid eating to the point of fullness
Hydration: Aim for at least 2 L of fluids per day, Sip water consistently throughout the day rather than drinking large amounts at once
Avoid: Skipping meals, which can worsen nausea later
Mild to moderate nausea
Nutrition: Switch to smaller, more frequent meals — aim for 5–6 small meals rather than 3 large ones, Choose bland, easy-to-digest foods: dry crackers, plain rice, plain bread, boiled potato, Eat slowly and chew thoroughly, Prioritise protein where tolerated: boiled eggs, plain chicken, Greek yoghurt, Avoid eating within 2–3 hours of bedtime
Hydration: Sip cool or room-temperature water frequently — small amounts every 15–20 minutes, Try chilled herbal teas (ginger or peppermint) which some people find settling, Electrolyte drinks (low sugar) can help if fluid intake is reduced
Avoid: High-fat or fried foods, Spicy foods, Strong food odours where possible, Carbonated drinks, Alcohol, Large meal portions
⚠ If nausea at this level persists for more than 3–4 days after a dose, mention it to your prescriber at your next contact.
Moderate to severe nausea
Nutrition: Focus on what you can tolerate — even small amounts of plain food are helpful, Try dry crackers or plain toast before getting out of bed if morning nausea is prominent, Cold foods (e.g. chilled fruit, yoghurt) may be better tolerated than hot meals, Sip a high-protein supplement drink if solid food is not tolerable
Hydration: Prioritise fluids above solid food if you cannot eat, Oral rehydration solutions (e.g. Hydralyte) can help maintain electrolyte balance, Sip 30–60 mL every 10–15 minutes if larger amounts trigger vomiting
Avoid: Fatty, fried, or rich foods, Dairy if it worsens symptoms for you, Eating while lying down, Strong smells
⚠ Contact your prescriber promptly — persistent severe nausea may warrant a dose review or anti-nausea support. Do not allow yourself to become significantly dehydrated.
Severe nausea with or without vomiting
Nutrition: Do not force food — focus entirely on fluid replacement, When able, try small amounts of plain, bland food
Hydration: Active hydration is the priority — sip fluids continuously, Seek medical attention if you cannot keep fluids down for more than 12 hours
Avoid: All foods until vomiting has settled, Any drinks with strong flavours or high sugar content if vomiting is active
⚠ Seek urgent medical attention if you are unable to keep down any fluids, show signs of dehydration (dizziness, dark urine, rapid heart rate), or if vomiting is accompanied by severe abdominal pain. Contact your prescriber or go to an urgent care centre.
Constipation
Minimal or no constipation
Nutrition: Maintain regular fibre intake from vegetables, fruit, legumes, and wholegrains, Keep meal timing consistent
Hydration: Aim for at least 2–2.5 L of fluids per day, Warm fluids in the morning (e.g. warm water with lemon) may support bowel regularity
Avoid: Prolonged periods of physical inactivity
Mild to moderate constipation
Nutrition: Increase dietary fibre gradually: add vegetables, legumes, oats, and fruit (kiwifruit and prunes are particularly effective), Eat at regular times each day to encourage bowel rhythm, Include flaxseeds or psyllium husk (start with 1 tsp/day and increase slowly)
Hydration: Increase fluid intake to at least 2.5–3 L/day — fibre works best with adequate hydration, A large glass of water first thing in the morning can help stimulate bowel activity, Warm herbal teas or warm water throughout the day
Avoid: Low-fibre, highly processed foods, Excessive dairy if it seems to worsen symptoms, Reducing fluid intake
⚠ If mild constipation persists beyond 5–7 days, mention it to your prescriber — they may suggest a gentle, osmotic laxative such as macrogol (Movicol/Osmolax).
Moderate to severe constipation
Nutrition: Prioritise high-fibre foods at every meal, Prunes, kiwifruit (2 per day), and pears are evidence-supported options, Avoid adding excessive supplemental fibre without adequate fluid — this can worsen blockage
Hydration: Increase fluids to 3 L+ per day if tolerated, Warm water or herbal tea on waking
Avoid: Straining excessively, Delaying the urge to use the bathroom, High-fat, low-fibre foods
⚠ Contact your prescriber — they may recommend an osmotic laxative or stool softener. Do not use stimulant laxatives without prescriber guidance.
Severe constipation or no bowel movement for 5+ days
Nutrition: Focus on fluids and light, easy-to-digest foods, Avoid high-fibre foods until the acute episode resolves — bulk fibre without passage can worsen discomfort
Hydration: Maximise fluid intake within tolerated limits
Avoid: Any foods likely to increase bulk without relief
⚠ Contact your prescriber promptly. Severe constipation — particularly if accompanied by abdominal pain, bloating, or nausea — requires medical assessment. Seek urgent care if you have significant abdominal pain or have not had a bowel movement for more than 5–7 days.
Appetite
Very low or absent appetite
Nutrition: Even if you are not hungry, aim to eat small amounts of protein-rich food every 3–4 hours, Liquid nutrition (e.g. protein shakes, smoothies with protein powder) can help meet nutritional needs when solid food is unappealing, Focus on nutrient density over quantity — every mouthful should count, Examples: Greek yoghurt, eggs, cottage cheese, nut butters, tinned fish
Hydration: Do not rely on thirst — set reminders to sip fluids throughout the day, Adding a small amount of electrolyte powder to water can help with palatability and electrolyte balance
Avoid: Going more than 4–5 hours without any nutritional intake, Empty-calorie foods that displace protein and micronutrients
⚠ If you are unable to meet minimum nutritional needs for more than 2–3 days, contact your prescriber — a dietitian referral or dose review may be warranted.
Noticeably reduced appetite
Nutrition: Use structured mealtimes rather than eating to hunger cues — hunger signals are intentionally blunted by the medication, Aim for protein at every meal and snack, Use a plate method: half non-starchy vegetables, a quarter protein, a quarter wholegrain or starchy vegetable, Plan meals in advance so nutritional quality is maintained even with low appetite
Hydration: Aim for 2–2.5 L of fluids daily, Drink fluids between meals rather than immediately before, to preserve limited appetite for food
Avoid: Skipping meals entirely, Filling up on fluids or low-nutrient snacks at the expense of meals
Appetite largely preserved or returning
Nutrition: Continue to choose nutrient-dense meals, Be mindful of portion sizes — the appetite-suppressing effect may vary across the dose cycle
Hydration: Maintain 2–2.5 L of fluids daily
Avoid: Ultra-processed, high-fat, or high-sugar foods which may worsen GI side effects
Food guidance by situation
Prefer: Plain crackers, dry toast, or plain rice, Boiled or steamed chicken or fish, Plain boiled potato or sweet potato, Cold or room-temperature foods (often better tolerated than hot meals), Ginger tea or peppermint tea (small sips), Greek yoghurt if dairy is tolerated, Banana or other low-acid fruit
Limit: Dairy (if it worsens symptoms), Fruit juice and acidic drinks, Caffeine
Avoid: Fried or high-fat foods, Spicy foods, Alcohol, Carbonated drinks, Strong food odours, Large meal portions
Gastric emptying is slowed by GLP-1/GIP receptor activation. High-fat and large-volume meals remain in the stomach longer, worsening nausea. Bland, low-fat, small-portion meals reduce gastric distension and symptom severity.
Prefer: High-fibre vegetables (broccoli, spinach, carrots, peas), Legumes (lentils, chickpeas, black beans), Wholegrains (oats, brown rice, wholegrain bread), Kiwifruit (2 per day — evidence-supported for bowel regularity), Prunes or prune juice (small amounts), Flaxseeds or psyllium husk (start with 1 tsp/day), Warm fluids — especially on waking
Limit: White bread and refined grain products, Processed snack foods, Cheese and full-fat dairy (in large quantities)
Avoid: Very low-fibre, highly processed foods as dietary staples
GLP-1 receptor agonism reduces gut motility, increasing constipation risk. Dietary fibre combined with adequate fluid intake supports bowel regularity. Fibre supplementation without sufficient hydration can paradoxically worsen constipation.
Prefer: Protein-dense, small-portion foods: eggs, Greek yoghurt, cottage cheese, tinned fish, tofu, Nutrient-dense smoothies or shakes with added protein powder, Nut butters (small amounts — energy and protein dense), Fortified foods where appropriate, Soft, easy-to-eat foods if chewing feels effortful
Limit: High-volume, low-nutrient foods that fill without delivering nutrition, Liquid calories from sugary drinks that displace food
Avoid: Skipping all meals — even small amounts of nutrition matter, Ultra-processed snack foods as primary nutrition source
Significant appetite suppression is an expected pharmacological effect of this triple receptor agonist, particularly at higher doses. When appetite is very low, nutritional quality must compensate for reduced quantity to avoid micronutrient deficiencies and muscle loss.
Prefer: Smaller, more frequent meals throughout the day, Low-fat protein sources, Easy-to-digest carbohydrates: plain rice, oats, boiled potato, Soft cooked vegetables
Limit: Large meal portions, High-fat meals, New foods that could confound GI symptom attribution
Avoid: Alcohol — which may worsen GI side effects and interact with glucagon receptor signalling, Rich, creamy, or fried meals in the 48 hours following a dose increase
GI side effects are typically most prominent in the first few days after a dose escalation, coinciding with rising drug concentrations (tmax 24–72 h). Proactively reducing gastric load during this window can meaningfully reduce nausea severity.
Prefer: Small meals or snacks only for the first 48–72 hours post-dose, Room-temperature or chilled foods, Ginger-containing foods or teas, Plain crackers or dry cereal
Limit: Full-sized meals — keep portions at roughly half of usual
Avoid: Fatty takeaway or restaurant meals, Alcohol, Carbonated beverages, Spicy or heavily seasoned foods
Peak drug concentration (tmax 24–72 h) is when nausea is most likely. Pre-planning light, bland meals for the 72 hours after each injection reduces GI symptom burden.
Prefer: Smaller meal portions eaten upright, Low-acid foods: oats, banana, melon, boiled vegetables, lean protein, Alkaline water if tolerated
Limit: Tomato-based sauces, Citrus fruits and juices, Caffeine and coffee, Chocolate, Mint (paradoxically can worsen reflux in some people)
Avoid: Eating within 2–3 hours of lying down, High-fat meals, Alcohol, Carbonated drinks
Slowed gastric emptying caused by GLP-1 agonism can worsen gastro-oesophageal reflux. Reducing gastric acid triggers and keeping the stomach from overfilling are the primary dietary strategies.
What to track
Suggested check-in cadence: dose day plus 2.
How would you rate your nausea right now? (0 = none, 10 = the worst imaginable)
scale 0 10
How would you rate your appetite right now? (0 = no appetite at all, 10 = completely normal appetite)
scale 0 10
How would you rate your energy levels today? (0 = no energy, 10 = normal energy for you)
scale 0 10
Have you experienced constipation or difficulty with bowel movements since your last dose? (0 = none, 10 = severe)
scale 0 10
Approximately how many litres of fluid have you had today? (L)
decimal
What is your weight this morning (before eating or drinking, after using the bathroom)? (kg)
decimal
Did you notice any redness, swelling, or pain at the injection site after this week's dose?
boolean
How many times have you vomited since your last dose? (Enter 0 if none) (episodes)
integer
Have you had any abdominal (belly) pain since your last dose? (0 = none, 10 = severe)
scale 0 10
If you are monitoring your blood glucose, what was your fasting reading this morning? (mmol/L)
decimal
Was this week's dose taken on your usual scheduled day?
boolean
Is there anything else you'd like to flag — any new or unusual symptoms since your last dose?
text
Take this to your appointment
Medication context: Investigational GLP-1 / GIP / glucagon triple receptor agonist (retatrutide) — Phase 3 trials ongoing; not TGA/FDA/MHRA/EMA approved
Key metrics: Current weekly dose (mg) and number of weeks on treatment, Total weight change since starting (kg and %), Weekly weight trend over the past 4 weeks (kg), Average daily fluid intake (L), Peak nausea score (0–10) since last review, Peak abdominal pain score (0–10) since last review, Constipation severity score (0–10) and days since last bowel movement, Number of vomiting episodes since last review, Fasting blood glucose readings (mmol/L) if monitored, Energy level score (0–10) average over past week, Injection-site reactions reported (yes/no and description), Any missed or delayed doses since last review, Any new medications or supplements commenced since last review
Relevant symptoms: Nausea severity and frequency, Vomiting episodes, Constipation — frequency and severity, Diarrhoea (if present), Gastro-oesophageal reflux or heartburn, Abdominal pain — location, character, radiation, Injection-site reactions, Dizziness or light-headedness (especially postural), Signs or symptoms of hypoglycaemia (if on concurrent glucose-lowering agents), Neck lump, hoarseness, or dysphagia, Mood or psychological wellbeing changes, Fatigue or unexplained low energy, Changes in appetite relative to expected medication effect, Visual changes
Safety and interactions
Share this information with your prescriber for personalised care decisions.
Red-flag symptoms — seek urgent care
- Severe or persistent abdominal pain — especially pain radiating to the backEmergencySevere abdominal pain — particularly pain that spreads to your back, or pain accompanied by vomiting — may be a sign of pancreatitis, a rare but serious condition. Stop eating and drinking and seek emergency medical care immediately. Tell the treating clinician you are using retatrutide.
- Lump or swelling in the neck, difficulty swallowing, or persistent hoarse voiceUrgent careA new lump in your neck, hoarseness, or difficulty swallowing may — in rare cases — be associated with thyroid changes. Please contact your prescriber urgently or attend an urgent care centre. Tell them you are taking retatrutide.
- Signs of severe dehydration — dizziness, dark urine, rapid heartbeat, inability to keep fluids downUrgent careIf you are unable to keep fluids down for more than 12 hours, feel dizzy when standing, have a rapid heartbeat, or your urine is very dark, you may be becoming dehydrated. Please seek urgent medical care. Dehydration is a serious complication of prolonged nausea or vomiting.
- Symptoms of low blood sugar — shakiness, sweating, confusion, rapid heartbeat (particularly if using concurrent glucose-lowering medications)Contact prescriberRetatrutide has glucose-lowering effects, particularly when used alongside other medications such as insulin or sulfonylureas. If you experience shakiness, cold sweats, confusion, or a racing heart, check your blood glucose if you are able to, and contact your prescriber. If symptoms are severe, seek emergency care.
- Allergic reaction — rash, hives, swelling of the face or throat, difficulty breathingEmergencySigns of a serious allergic reaction include skin rash or hives, swelling of your face, lips, or throat, or difficulty breathing. This is a medical emergency — call 000 (Australia) or your local emergency number immediately.
- Persistent vomiting — unable to keep any food or fluid down for more than 12 hoursUrgent careIf you have been vomiting repeatedly and cannot keep any food or fluids down for more than 12 hours, please seek urgent medical attention. Prolonged vomiting can lead to dangerous dehydration and electrolyte imbalances.
- Significant changes in vision or unexplained eye symptomsContact prescriberRapid changes in blood glucose levels can sometimes affect vision. If you notice sudden blurring or other visual changes, contact your prescriber promptly for assessment.
- New or worsening mood changes, thoughts of self-harm, or significant psychological distressContact prescriberIf you notice significant changes in your mood, feel very low, or have any thoughts of harming yourself, please reach out to your prescriber or a mental health professional promptly. In an emergency, call Lifeline on 13 11 14 (Australia) or your local crisis service.
- Severe or persistent GI symptoms. Repeated vomiting, dehydration, or severe persistent abdominal pain needs urgent medical assessment.
- Severe abdominal pain. Stop dosing and seek urgent medical assessment for severe or persistent abdominal pain, especially if it radiates to the back or is accompanied by repeated vomiting - possible pancreatitis.
- Signs of severe allergic reaction. Seek emergency care for swelling of the face, lips, tongue or throat, breathing difficulty, fainting, or widespread rash after dosing.
- Thyroid tumour risk (MTC / MEN2). Retatrutide has not been tested in people with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN2), and these individuals were excluded from Phase 2 trials. Tell your prescriber immediately if you notice a lump or swelling in your neck, hoarseness, difficulty swallowing, or shortness of breath.
- Pancreatitis symptoms. Seek urgent medical attention if you develop severe, persistent pain in your abdomen or back, with or without vomiting — these may be signs of pancreatitis. People with a prior history of pancreatitis were excluded from Phase 2 trials.
- Severe allergic reaction. Seek emergency care immediately if you experience swelling of the face, lips, tongue, or throat, difficulty breathing, a rapid heartbeat, or a widespread rash after your injection — these may signal a serious allergic reaction.
- Dehydration from severe vomiting or diarrhoea. Prolonged nausea, vomiting, or diarrhoea can lead to dehydration. Contact your prescriber promptly if you are unable to keep fluids down for more than 24 hours, feel dizzy, or notice a marked decrease in urination.
- Dehydration from gastrointestinal side effects. Persistent vomiting or diarrhoea can lead to dehydration, which may be serious. If you are unable to keep fluids down, feel dizzy or lightheaded, or notice very dark urine, contact your prescriber urgently or seek medical attention.
Structured warnings
Investigational medicine
Retatrutide is not approved by major regulators. Dosing and monitoring in published data come from clinical trial protocols, not a prescribing label.
Prescriber-led titration only
The 2-12 mg weekly schedules are trial references. Do not self-escalate or skip escalation steps without prescriber or trial-site direction.
Severe or persistent GI symptoms
Repeated vomiting, dehydration, or severe persistent abdominal pain needs urgent medical assessment.
Severe abdominal pain
Stop dosing and seek urgent medical assessment for severe or persistent abdominal pain, especially if it radiates to the back or is accompanied by repeated vomiting - possible pancreatitis.
Signs of severe allergic reaction
Seek emergency care for swelling of the face, lips, tongue or throat, breathing difficulty, fainting, or widespread rash after dosing.
Thyroid tumour risk (MTC / MEN2)
Retatrutide has not been tested in people with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN2), and these individuals were excluded from Phase 2 trials. Tell your prescriber immediately if you notice a lump or swelling in your neck, hoarseness, difficulty swallowing, or shortness of breath.
Pancreatitis symptoms
Seek urgent medical attention if you develop severe, persistent pain in your abdomen or back, with or without vomiting — these may be signs of pancreatitis. People with a prior history of pancreatitis were excluded from Phase 2 trials.
Severe allergic reaction
Seek emergency care immediately if you experience swelling of the face, lips, tongue, or throat, difficulty breathing, a rapid heartbeat, or a widespread rash after your injection — these may signal a serious allergic reaction.
Dehydration from severe vomiting or diarrhoea
Prolonged nausea, vomiting, or diarrhoea can lead to dehydration. Contact your prescriber promptly if you are unable to keep fluids down for more than 24 hours, feel dizzy, or notice a marked decrease in urination.
Dehydration from gastrointestinal side effects
Persistent vomiting or diarrhoea can lead to dehydration, which may be serious. If you are unable to keep fluids down, feel dizzy or lightheaded, or notice very dark urine, contact your prescriber urgently or seek medical attention.
Gastrointestinal side effects
Nausea, vomiting, diarrhoea, and constipation are the most commonly reported side effects in Phase 2 trials. These effects are usually mild to moderate and tend to be most noticeable in the days after a dose increase. Eating smaller meals and avoiding high-fat or spicy foods may help.
Investigational drug — not TGA/FDA/MHRA/EMA approved
Retatrutide is not yet approved by any major regulatory authority. It is currently available only through clinical trials or compounding pharmacies under prescriber supervision. Long-term safety and efficacy data are still being gathered in ongoing Phase 3 trials.
Investigational status — not TGA, FDA, MHRA, or EMA approved
Retatrutide is currently an investigational medicine. It has not been approved by the TGA, FDA, MHRA, or EMA. Long-term safety and efficacy data are still being gathered in Phase 3 trials. Discuss the benefits and risks with your prescriber before starting.
Use during pregnancy or breastfeeding
Retatrutide was excluded from use in pregnancy and breastfeeding in Phase 2 trials; its safety in these settings has not been established. Speak with your prescriber before using this medicine if you are pregnant, planning to become pregnant, or breastfeeding.
Indication and approval status
Obesity, type 2 diabetes, and metabolic disease indications remain under clinical investigation.
Clinical trial participants only; no approved prescribing population.
Who should not take this
Retatrutide is investigational and has not been approved by the TGA, FDA, MHRA, or EMA — access is currently limited to clinical trials. Phase 2 trial protocols excluded participants with: • Personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN2) • Severe gastrointestinal disease including gastroparesis • A history of pancreatitis • Active or recent eating disorder • Type 1 diabetes • Pregnancy or breastfeeding • Significant cardiovascular events in the prior 3 months Talk with your prescriber about whether any of these apply to you.
Known interactions
- Insulin and sulfonylureassignificant
Increased risk of hypoglycaemia when combined with agents that stimulate insulin secretion or deliver exogenous insulin. Prescribers typically reduce insulin or sulfonylurea doses when initiating or escalating retatrutide.
- Oral medicines with a narrow therapeutic indexmoderate
Retatrutide delays gastric emptying, which can alter the absorption rate of some orally administered medicines. Particular care is warranted for drugs such as warfarin and certain anti-epileptics.
- Oral contraceptivesmoderate
Delayed gastric emptying may transiently affect oral contraceptive absorption during dose escalation. Consider additional non-hormonal contraception around dose changes — discuss with your prescriber.
- Alcoholmoderate
Alcohol can worsen nausea, dehydration, and the risk of hypoglycaemia when combined with GLP-1 family agents. Moderation is advised.
Missed-dose guidance
No approved label missed-dose rule exists for retatrutide.
Follow the trial site, prescriber, or dispensing pharmacy instructions; do not double-dose.
If you miss your usual weekly injection day, administer your dose as soon as you remember — provided your next scheduled dose is at least 72 hours (3 days) away. If fewer than 72 hours remain before your next scheduled dose, omit the missed dose and resume your regular weekly schedule. Do not administer two doses within the same 72-hour window.
After a missed dose, return to your regular once-weekly injection day. Contact your prescriber if you are unsure whether to administer a missed dose, particularly during a dose-escalation period.
If you miss your once-weekly dose and it has been fewer than 3 days (72 hours) since your scheduled injection day, administer the missed dose as soon as you remember. Then resume your regular weekly schedule from that point.
If more than 3 days (72 hours) have passed since the missed dose, omit that dose entirely and administer your next dose on your regularly scheduled day. Do not administer two doses within the same 3-day window.
When to seek help
Nausea that prevents eating or hydration, or worsens after escalation.
Contact the prescriber or trial site before the next escalation.
Repeated vomiting, dizziness, reduced urination, or inability to keep fluids down.
Seek urgent assessment for dehydration and dose review.
Severe persistent abdominal pain, especially with vomiting or pain radiating to the back.
Seek urgent medical advice.
Side-effect timing windows
Population typicals from trial data — individual experience varies.
Nausea
Onset 1–24 h · Peak 24–72 h · Resolves ~14d
Trial data; intensity scales with dose escalation step.
Vomiting
Onset 2–24 h · Peak 24–72 h · Resolves ~7d
Diarrhoea
Onset 4–48 h · Peak 24–96 h · Resolves ~7d
Trial data; scales with dose escalation step.
Constipation
Onset 24–96 h · Peak 48–168 h · Resolves ~7d
Reported in Phase 2 data. Gastric emptying is slowed by GLP-1 and GIP receptor agonism. Adequate fluid and fibre intake may help.
Injection-site reaction
Onset 0.5–6 h · Peak 1–12 h · Resolves ~2d
Localised redness, swelling, or itching at the injection site. Generally mild and self-limiting. Rotating injection sites helps minimise recurrence. Notify your prescriber if reactions worsen or persist beyond a few days.
Decreased appetite
Onset 2–24 h · Peak 12–48 h · Resolves —
A pharmacologically expected effect of GLP-1, GIP, and glucagon receptor agonism. Appetite suppression may persist throughout treatment. Ensure adequate nutritional intake; discuss with your prescriber if eating becomes very difficult.
Eructation (burping)
Onset 1–12 h · Peak 2–24 h · Resolves ~2d
Commonly associated with GLP-1 receptor agonist class effects due to slowed gastric emptying. Usually mild and transient.
Approved injection sites
Abdomen
Trial protocol rotates weekly across abdomen, thigh and upper arm; follow trial-site instruction.
Avoid: Investigational use only - follow trial-site rotation directions.
Thigh
Front of the thigh.
Upper arm
Back of the upper arm.
Structured storage
lyophilized vial
before reconstitution
-20 C or colder where supplied as research/compounded lyophilized powder
Follow the dispensing pharmacy or trial-site instructions; allow vial to reach room temperature before reconstitution.
reconstituted vial
after reconstitution
Refrigerate at 2-8 C
Use within 4 weeks unless the pharmacy or trial protocol gives a shorter window.
Maintain strict sterile technique and discard if cloudy, particulate, or discoloured.
Storage and handling
As an investigational biologic, storage is governed by the trial protocol or pharmacy you receive the product from. GLP-1 family injectables in this class are typically: • Stored refrigerated at 2–8°C (36–46°F) • Kept in the original packaging to protect from light • Not frozen — freezing can damage the active peptide • Allowed to reach room temperature before injection (check the product instructions) Always follow the storage and handling instructions supplied by your prescriber or trial site.
Research evidence
Published studies, labels, regulator pages, and curated protocol sources connected to this profile.
API source references
Retatrutide obesity Phase 2 trial
Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity. N Engl J Med. 2023.
Open source ↗Retatrutide type 2 diabetes Phase 2 trial
Rosenstock J et al. Retatrutide for people with type 2 diabetes. Lancet. 2023.
Open source ↗Retatrutide 20 mg vial PeptideDosages protocol
Editorial protocol page used as a manually reviewed structure checklist; not a prescribing label.
Open source ↗Retatrutide 5 mg vial PeptideDosages protocol
Editorial research protocol page for Retatrutide 5 mg vial; not a prescribing label.
Open source ↗Retatrutide 10 mg vial PeptideDosages protocol
Editorial research protocol page for Retatrutide 10 mg vial; not a prescribing label.
Open source ↗Retatrutide 30 mg vial PeptideDosages protocol
Editorial research protocol page for Retatrutide 30 mg vial; not a prescribing label.
Open source ↗Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo-and-active-controlled, parallel-group, phase 2 trial
Human trial · 2023 · The Lancet · n=281 · Adults with type 2 diabetes, HbA1c 7.0–10.5%, on diet/exercise or stable metformin
281 adults with type 2 diabetes were randomised to retatrutide (0.5, 4, 8, or 12 mg weekly subcutaneously, with titration), dulaglutide 1.5 mg weekly, or placebo, and followed for 36 weeks. HbA1c reductions were dose-dependent, reaching −2.02% at 12 mg retatrutide. Mean body-weight changes at week 36 ranged from −3.19% at 0.5 mg to −16.94% at 12 mg.
Reported outcomes
- comparator: Retatrutide 8 mg and 12 mg produced larger HbA1c and weight reductions than dulaglutide 1.5 mg weekly. (Secondary)
- weight_loss: Mean body-weight reduction of 16.94% at 12 mg weekly retatrutide at 36 weeks in type 2 diabetes. (Secondary)
- hba1c_reduction: HbA1c reduction of up to −2.02% at 12 mg weekly retatrutide over 36 weeks in adults with type 2 diabetes. (Primary efficacy outcome)
Reported dosage
- 8 mg · once weekly subcutaneous · 36 weeks — Higher dose arm; scheduled titration.
- 12 mg · once weekly subcutaneous · 36 weeks — Highest dose arm in the T2D Phase 2.
- 4 mg · once weekly subcutaneous · 36 weeks — Mid dose arm; scheduled titration.
- 0.5 mg · once weekly subcutaneous · 36 weeks — Lowest dose arm in the T2D Phase 2.
Triple–Hormone-Receptor Agonist Retatrutide for Obesity — a Phase 2 Trial
Human trial · 2023 · New England Journal of Medicine · n=338 · Adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related condition, without diabetes
338 adults were randomised to placebo or retatrutide at 1, 4, 8, or 12 mg once-weekly subcutaneously (with lower starting doses and scheduled escalation), and followed for 48 weeks. At week 48, least-squares mean percent change in body weight was −24.2% in the 12 mg group versus −2.1% with placebo. Most adverse events were gastrointestinal and mild-to-moderate.
Reported outcomes
- cardiometabolic: Favourable changes in HbA1c, lipids, and systolic blood pressure were reported across dose arms. (Secondary)
- weight_loss: Mean body-weight reduction of 24.2% at 48 weeks on 12 mg weekly retatrutide, vs 2.1% on placebo. (Primary efficacy outcome)
- weight_loss: Dose-response was observed across 1, 4, 8, and 12 mg arms with no apparent plateau at 48 weeks. (Secondary)
Reported dosage
- 8 mg · once weekly subcutaneous · 48 weeks — Higher dose arm; scheduled titration with checkpoints at 2, 4, and 6 mg.
- 12 mg · once weekly subcutaneous · 48 weeks — Highest dose arm in the trial; titration continued through 2, 4, 6, and 9 mg before reaching 12 mg.
- 1 mg · once weekly subcutaneous · 48 weeks — Lowest dose arm; all participants started at 2 mg for 4 weeks before down- or up-titration.
- 4 mg · once weekly subcutaneous · 48 weeks — Mid dose arm; scheduled titration up from 2 mg.
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