Informational only. Not medical advice.INFORMATIONAL PLATFORM ONLY — NOT MEDICAL ADVICE, DIAGNOSIS, OR TREATMENT
Informational only. Not medical advice.INFORMATIONAL PLATFORM ONLY — NOT MEDICAL ADVICE, DIAGNOSIS, OR TREATMENT
Retatrutide (LY3437943) is Eli Lilly’s investigational triple-agonist peptide targeting GLP-1, GIP, and glucagon receptors. This page summarizes the dosing schedule used in the Phase 2 TRIUMPH obesity trial, the reconstitution math for common vial sizes, and how the schedule compares to approved GLP-1 and dual-agonist medications. It is a research reference, not medical advice.
The Phase 2 TRIUMPH trial used a 4-week-per-step titration cadence to reach target dose. Starting dose was 2mg weekly. Participants advanced to the next dose after 4 weeks on the prior dose, assuming tolerability. The schedule below reflects the 12mg target arm that produced the highest weight loss at 48 weeks.
| Week | Dose | Frequency | Notes |
|---|---|---|---|
| 1–4 | 2 mg | Weekly SC | Starting dose. GI side effects typically peak during this window. |
| 5–8 | 4 mg | Weekly SC | First escalation. Hold if significant nausea persists. |
| 9–12 | 6 mg | Weekly SC | Optional intermediate step if tolerability is marginal. |
| 13–16 | 8 mg | Weekly SC | 8mg arm in TRIUMPH produced 22.8% weight loss at 48 weeks. |
| 17–20 | 10 mg | Weekly SC | Optional intermediate step toward 12mg target. |
| 21+ | 12 mg | Weekly SC | Maintenance target. 24.2% weight loss at 48 weeks in trial. |
TRIUMPH also included 1mg, 4mg, and 8mg target arms with no escalation beyond the assigned target. The stepwise 4-week cadence above follows the 12mg target arm. All injections were subcutaneous, rotating between abdomen, thigh, and upper arm.
| Compound | Mechanism | Starting dose | Max dose | Peak weight loss |
|---|---|---|---|---|
| Retatrutide | GLP-1 / GIP / Glucagon | 2 mg/wk | 12 mg/wk | 24.2% at 48 wk |
| Tirzepatide | GLP-1 / GIP | 2.5 mg/wk | 15 mg/wk | 22.5% at 72 wk |
| Semaglutide | GLP-1 | 0.25 mg/wk | 2.4 mg/wk | 15.0% at 68 wk |
| Liraglutide | GLP-1 | 0.6 mg/day | 3.0 mg/day | 8.0% at 56 wk |
Weight loss percentages are from published Phase 2 and Phase 3 trials in participants with obesity and without type 2 diabetes. Cross-trial comparisons are approximate; head-to-head trial data between retatrutide and other agents is pending.
Retatrutide is typically sold lyophilized in 5mg, 10mg, 15mg, or 20mg vials. The bacteriostatic water (BAC water) volume you mix with determines the concentration, which determines how many milliliters correspond to a given weekly dose. The table below shows injection volumes for the most common combinations.
| Vial | BAC water | Concentration | 2 mg dose | 4 mg dose | 8 mg dose | 12 mg dose |
|---|---|---|---|---|---|---|
| 10 mg | 1 mL | 10 mg/mL | 0.20 mL | 0.40 mL | 0.80 mL | n/a |
| 10 mg | 2 mL | 5 mg/mL | 0.40 mL | 0.80 mL | n/a | n/a |
| 15 mg | 1.5 mL | 10 mg/mL | 0.20 mL | 0.40 mL | 0.80 mL | 1.20 mL |
| 20 mg | 2 mL | 10 mg/mL | 0.20 mL | 0.40 mL | 0.80 mL | 1.20 mL |
The Phase 2 TRIUMPH trial reported side-effect frequency across dose arms. Most events were gastrointestinal and peaked during titration, consistent with the class of GLP-1-based medications. Numbers below are for the 12mg target arm.
Nausea
~50%
Diarrhea
~35%
Vomiting
~25%
Constipation
~15%
Heart rate increase
+6–7 bpm
AE discontinuation
6–13%
Research protocols typically run baseline labs before starting, mid-cycle labs around week 12, and follow-up labs 4 weeks after the final dose. HbA1c and fasting glucose capture glycemic response, liver enzymes flag hepatic stress from glucagon-arm activity, and heart rate plus lipid panel capture the cardiovascular signature.
The Phase 2 TRIUMPH trial started participants at 2mg weekly for the first 4 weeks, then escalated every 4 weeks. The low-dose arm (2mg) was used as an active comparator and showed meaningful weight loss on its own. Most compounded protocols follow the trial's escalation schedule: 2mg → 4mg → 8mg → 12mg at 4-week intervals, mirroring how tirzepatide is titrated to manage gastrointestinal side effects.
The highest dose studied in the Phase 2 obesity trial was 12mg weekly. This dose produced 24.2% mean body weight loss at 48 weeks — the largest reduction reported for any anti-obesity medication in clinical trials. An 8mg arm was also tested and produced 22.8% loss. Phase 3 trials (TRIUMPH-1, TRIUMPH-2, TRIUMPH-4) use the same dose range.
4 weeks. The TRIUMPH trial held each dose for 4 weeks before stepping up, matching the titration cadence used for tirzepatide (Mounjaro/Zepbound). Faster titration is associated with more gastrointestinal side effects without better weight loss outcomes, so the 4-week hold is not arbitrary.
The numerical doses look similar (both ranges span roughly 2–15mg weekly), but the titration endpoints differ: tirzepatide caps at 15mg weekly in obesity trials while retatrutide was studied up to 12mg. Retatrutide produces greater weight loss per milligram because the glucagon-receptor arm adds thermogenesis on top of GLP-1/GIP appetite suppression. Side-effect profiles are similar, with nausea the most common GI symptom during titration.
Semaglutide tops out at 2.4mg weekly for weight management (Wegovy). Retatrutide's 12mg weekly dose is 5x higher numerically, but the molecules are distinct triple-agonist vs GLP-1 monoagonist. In cross-trial comparisons retatrutide produced roughly 1.5x the weight loss of semaglutide at peak doses. Semaglutide's titration schedule also differs: 0.25 → 0.5 → 1.0 → 1.7 → 2.4mg, stepping up every 4 weeks.
There is no single correct concentration — it depends on vial size and desired injection volume. A 10mg vial reconstituted with 2mL of bacteriostatic water yields 5mg/mL, meaning a 4mg dose requires 0.8mL. A 10mg vial with 1mL of BAC water yields 10mg/mL, meaning a 4mg dose requires 0.4mL. Use our reconstitution calculator to compute injection volume for any combination of vial mg, BAC water mL, and target dose.
Eli Lilly's Phase 3 TRIUMPH program began in 2023 with readouts expected in 2026 and a potential FDA approval in late 2026 or 2027 depending on trial outcomes and submission timing. Until approval, retatrutide is research-only and not available from licensed pharmacies. Any product labeled as retatrutide is either a research chemical or compounded — neither has been evaluated by the FDA for safety or efficacy.
At the 12mg dose in the Phase 2 trial, nausea occurred in approximately 50% of participants, diarrhea in 35%, vomiting in 25%, and constipation in 15%. Most GI events were mild to moderate and peaked during titration. Heart rate increased modestly across all doses (approximately 6–7 bpm at 12mg). Discontinuation due to adverse events was 6–13% across dose groups — comparable to tirzepatide at equivalent doses.
This guide provides informational research data only, not medical advice. Retatrutide is not FDA-approved. Consult a licensed healthcare provider before using any peptide.
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