> Note: PeptIQ is not a medical provider. This guide is educational. Retatrutide is an investigational drug: it is not FDA-approved, has no label, and cannot legally be compounded or sold for human use. Nothing here is a dosing recommendation. Talk with a licensed clinician about approved options.
Answer first: Retatrutide (Eli Lilly's LY3437943) is a once-weekly injectable peptide that activates three receptors at once: GIP, GLP-1 and glucagon. In Lilly's Phase 2 trial, the 12 mg group lost an average of 24.2% of body weight at 48 weeks, and the Phase 3 TRIUMPH program reported topline results in 2026. Lilly says it plans to file for U.S. approval in the first quarter of 2027. Until FDA acts, every "retatrutide" vial sold online is an unapproved, unverified product.
Retatrutide at a Glance
For a non-dosing introduction, read what retatrutide is: the triple agonist explained.
| What it is | A synthetic peptide agonist of the GIP, GLP-1 and glucagon receptors ("triple agonist") |
| Developer | Eli Lilly (code name LY3437943) |
| Status (Oct 2026) | Investigational. Not approved anywhere. Phase 3 TRIUMPH trials reported |
| Phase 2 result | Up to 24.2% mean weight loss at 48 weeks (12 mg group) vs 2.1% on placebo |
| Phase 3 (TRIUMPH-2 / -3, July 2026) | 20.8% in adults with obesity and type 2 diabetes; 22.6% in severe obesity with cardiovascular disease (12 mg arms, topline) |
| Planned filing | Lilly moved its U.S. submission target to Q1 2027 to finish the manufacturing package |
| Compounding | FDA has said retatrutide cannot be used in compounding under federal law |
| Approved alternatives | Semaglutide (Wegovy), tirzepatide (Zepbound), orforglipron (Foundayo), through a licensed clinician |
What Retatrutide Is and How It Works
Approved GLP-1 drugs act on one receptor (semaglutide) or two (tirzepatide adds GIP). Retatrutide adds a third: the glucagon receptor. The GLP-1 and GIP activity slows gastric emptying, lowers appetite and improves insulin response. Glucagon receptor activity is thought to raise energy expenditure and liver fat burning, which is why researchers expected (and saw) larger weight loss than with dual agonists.
Mechanism explainers: semaglutide vs tirzepatide vs retatrutide mechanisms, the 3D retatrutide explainer, and the retatrutide compound profile.
Retatrutide Dosing: What the Trials Reported
People searching "retatrutide dosing" usually want a starting dose. There isn't one to give: retatrutide has no label, and the trial regimens are not a personal protocol. What exists is trial-reported data, summarized here as published.
Phase 2 (NEJM, 2023)
In the Phase 2 obesity trial, 338 adults were randomized to once-weekly subcutaneous retatrutide or placebo for 48 weeks. The trial arms were:
| Trial arm (once weekly) | How the arm started | Mean weight change at 48 weeks |
|---|---|---|
| 1 mg | 1 mg | -8.7% |
| 4 mg | initial dose 2 mg or 4 mg, then escalated | -17.1% (combined 4 mg groups) |
| 8 mg | initial dose 2 mg or 4 mg, then escalated | -22.8% (combined 8 mg groups) |
| 12 mg | initial dose 2 mg, then escalated | -24.2% |
| Placebo | -2.1% |
Two findings from that paper matter for anyone reading dose charts online:
- Gastrointestinal side effects were the most common adverse events, were dose-related, and were partially mitigated by the lower 2 mg starting dose compared with starting at 4 mg.
- Heart rate rose in a dose-dependent way, peaked around week 24, and declined afterward.
Phase 3 (TRIUMPH program)
TRIUMPH-1 (NCT05929066), the pivotal obesity trial, finished its primary endpoint in April 2026. On July 23, 2026, Lilly reported that TRIUMPH-2 and TRIUMPH-3 met their primary endpoints, with 20.8% and 22.6% average weight loss in the 12 mg arms. Our July 2026 readout breakdown and TRIUMPH-1 tracking guide cover the numbers; the side-effects guide covers what the trials reported about nausea, dysesthesia (skin burning) and blood pressure.
Why that isn't a protocol
Trial participants were screened, monitored and escalated under a study design with a control group. They used Lilly's drug product, not a vial of unknown content. When a forum chart tells you to "start at 0.25 mg," it's describing a community habit, not a trial arm. The honest answer to "how much retatrutide should I take" is: that's a decision for a licensed clinician, and today no clinician can legally prescribe it.
Reconstitution Math (Arithmetic Only)
If you're tracking an investigational vial with a clinician, the arithmetic is the same as for any lyophilized peptide. The math tells you concentration; it does not tell you an amount to draw.
Concentration (mg/mL) = milligrams on the label ÷ milliliters of bacteriostatic water added.
On a U-100 insulin syringe, 100 units = 1 mL, so 10 units = 0.1 mL.
| Label | Water added | Concentration | 1 mg = | 10 units = |
|---|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 20 units | 0.5 mg |
| 5 mg | 2 mL | 2.5 mg/mL | 40 units | 0.25 mg |
| 10 mg | 1 mL | 10 mg/mL | 10 units | 1 mg |
| 10 mg | 2 mL | 5 mg/mL | 20 units | 0.5 mg |
| 20 mg | 2 mL | 10 mg/mL | 10 units | 1 mg |
| 20 mg | 4 mL | 5 mg/mL | 20 units | 0.25 mg |
Adding more water lowers the concentration, which makes small amounts easier to measure but changes every unit count. Recalculate any time the water volume changes. Use the calculator at the top of this page or the web reconstitution calculator, and see the vial-size companions: 10 and 20 mg vials and 30, 40 and 60 mg vials.
Handling basics
- Wipe both stoppers with alcohol.
- Add the water slowly down the glass wall, not onto the powder.
- Swirl or roll gently. Don't shake.
- Let it sit until clear. Cloudiness or particles mean something is wrong.
- Refrigerate after mixing.
There is no label to tell you how long a reconstituted retatrutide vial stays good. Community storage windows are unvalidated. Our shelf-life guide and reconstitution mistakes guide explain what is and isn't known.
Side Effects Reported in Trials
- Gastrointestinal: nausea, vomiting, diarrhea and constipation were the most common adverse events in Phase 2, mostly mild to moderate, dose-related, and more frequent during escalation.
- Heart rate: dose-dependent increases that peaked at week 24 and declined thereafter.
- Phase 3 signals: the TRIUMPH program reported dysesthesia (skin burning or tingling) and blood-pressure effects alongside GI events. Full breakdown: retatrutide side effects.
- Heat and dehydration: retatrutide, heat and side effects.
If you're experiencing side effects from any GLP-1 class drug, that's a conversation with a clinician, not a reason to change an amount on your own.
Where Approval Stands
- July 23, 2026: Lilly announced positive topline TRIUMPH-2 and TRIUMPH-3 results.
- Filing target: Lilly moved its planned Biologics License Application to Q1 2027 while it completes the manufacturing (CMC) package. Why that isn't a setback: BLA moves to Q1 2027.
- What a filing means: submission, FDA acceptance, review and a decision all come after. A Q1 2027 filing is not a 2027 approval.
- Counterfeits: Lilly has sued online sellers and FDA has sent warning letters to "research use only" vendors. Lab tests have found vials labeled retatrutide that contained other drugs. Read counterfeit retatrutide: Lilly lawsuits and FDA action before trusting any listing.
Every Retatrutide Guide on PeptIQ.io
Start here
- What the triple agonist does
- Semaglutide vs tirzepatide vs retatrutide mechanisms
- Retatrutide vs tirzepatide: clinical data
- Eloralintide vs retatrutide
Trials and status
