Retatrutide: Overview, Dosage, Side Effects & Research
The most powerful weight loss peptide in clinical development, targeting three metabolic receptors simultaneously.
Also known as: LY3437943, triple agonist peptide
What is Retatrutide?
Retatrutide is a triple agonist that simultaneously activates GIP (glucose-dependent insulinotropic polypeptide), GLP-1 (glucagon-like peptide-1), and glucagon receptors. This triple-action approach enhances insulin secretion, suppresses appetite, increases energy expenditure, and improves lipid metabolism more powerfully than dual or single agonists. The glucagon component drives thermogenesis and fat oxidation, while GLP-1 and GIP together manage glucose and satiety.
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Dosage Overview
| Level | Dose |
|---|---|
| Starting / Low | 1 mg |
| Typical / Maintenance | 8-12 mg |
| Maximum (studied) | 24 mg |
Administered as subcutaneous injection once weekly. Titrate slowly to minimize GI side effects. The TRIUMPH-1 trial used titration from 2mg up to 24mg over 24 weeks.
Full dosage guide with titration schedule →Side Effects
| Side Effect | Frequency |
|---|---|
| Nausea | common |
| Vomiting | common |
| Diarrhea | common |
| Constipation | common |
| Decreased appetite | common |
| Injection site reactions | common |
Clinical Research
24mg dose achieved mean body weight reduction of 24.2% at 48 weeks — the highest ever recorded for any injectable weight-loss drug in a clinical trial at the time.
Phase 3 trials ongoing. Expected to seek FDA approval in 2026–2027.
Best Used For
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Frequently Asked Questions
Is Retatrutide FDA approved?
No. As of 2026, Retatrutide is still in Phase 3 clinical trials. It is not yet FDA approved and is not legally available as a prescription medication in the US. Phase 3 trials are ongoing and FDA filing is anticipated in 2026–2027.
How does Retatrutide compare to Tirzepatide (Mounjaro/Zepbound)?
Retatrutide is a triple agonist (GIP + GLP-1 + glucagon) while Tirzepatide is a dual agonist (GIP + GLP-1). The added glucagon receptor activity in Retatrutide drives additional thermogenesis, which appears responsible for the greater weight loss observed in trials — 24.2% vs roughly 20–22% for Tirzepatide at maximum doses.
What is the expected dose of Retatrutide?
Clinical trials have used doses ranging from 1mg to 24mg weekly, injected subcutaneously. The 8mg, 12mg, and 24mg doses showed the strongest weight loss outcomes. Final approved dosing will depend on FDA approval decisions.
When will Retatrutide be available?
Eli Lilly, the developer, is expected to file for FDA approval in 2026–2027. If approved on a typical timeline, it could reach pharmacy shelves by 2027–2028.
Can I buy Retatrutide from a compounding pharmacy?
Because Retatrutide is not yet FDA approved, there is no FDA-approved reference product for compounders to reference. This makes it legally unavailable through standard compounding pathways that supply semaglutide and tirzepatide. Exercise extreme caution with any source claiming to sell it.
How much weight can you lose on Retatrutide?
In the TRIUMPH-1 Phase 2 trial (N=338, 48 weeks), participants on the 24mg dose lost a mean of 24.2% of body weight. At 12mg, the mean loss was 22.8%. At 8mg, 17.3%. For a 250-pound person, 24.2% equates to approximately 60.5 pounds lost. These results are from the highest dose group — individual outcomes vary based on dose, diet, activity level, and baseline metabolic health.
Is Retatrutide better than Ozempic (semaglutide)?
Based on available trial data, Retatrutide produces substantially greater weight loss than semaglutide. The STEP trials for Wegovy (semaglutide 2.4mg) showed ~15% average weight loss at 68 weeks, while TRIUMPH-1 showed 24.2% at 24mg retatrutide. However, semaglutide is FDA approved and commercially available, while retatrutide remains investigational. The mechanisms also differ: retatrutide targets three receptors (GLP-1, GIP, glucagon) versus semaglutide's single GLP-1 receptor target.
How long until Retatrutide starts working?
Based on TRIUMPH-1 data, meaningful weight loss begins within the first 8 weeks, even at lower titration doses. Participants on the 24mg arm showed approximately 6.2% weight reduction by week 8. The most rapid weight loss phase occurs between weeks 8 and 36, with results plateauing around weeks 36–48 as participants approach their new set point. Peak results appear at approximately 48 weeks of continuous treatment.
Does Retatrutide cause muscle loss?
TRIUMPH-1 showed a mean lean mass reduction of approximately 5% alongside total body weight loss. This is consistent with other GLP-class weight loss drugs. Fat mass loss was proportionally much larger, making the weight loss predominantly fat-preferential. Resistance training (2–3 sessions per week) combined with adequate protein intake (at minimum 0.8g/kg, ideally 1g/lb bodyweight) substantially reduces lean mass loss during treatment. The lean mass percentage can actually improve even as absolute lean mass decreases slightly.
What is Retatrutide's brand name?
Retatrutide does not yet have an FDA-approved brand name, as it has not completed Phase 3 trials. Eli Lilly has not announced a commercial brand name. The compound is identified in research by its code name LY3437943. When approved, it will receive a brand name — speculation has not been confirmed by Lilly.
How do you pronounce retatrutide?
Retatrutide is pronounced: reh-TAT-roo-tide. The emphasis falls on the second syllable (TAT). The name follows standard INN (International Nonproprietary Name) conventions for GLP-1 receptor agonist class drugs, which typically end in '-tide' or '-glutide'.
Is Retatrutide a GLP-3?
No — 'GLP-3' is a popular but technically imprecise label for Retatrutide. Retatrutide is classified as a GIP/GLP-1/glucagon triple receptor agonist. It activates three distinct receptors: GLP-1R (glucagon-like peptide-1 receptor), GIPR (glucose-dependent insulinotropic polypeptide receptor), and glucagon receptor. 'GLP-3' refers to a different endogenous peptide (also called oxyntomodulin in some contexts) with distinct biology. The 'GLP-3' label has been applied colloquially to retatrutide in consumer media but does not reflect its pharmacological classification.
How does Retatrutide compare to Tirzepatide weight loss?
In head-to-head trial data context: SURMOUNT-1 (tirzepatide, N=2,539, 72 weeks) showed maximum dose (15mg) achieving 22.5% mean weight loss. TRIUMPH-1 (retatrutide, N=338, 48 weeks) showed 24mg achieving 24.2% mean weight loss at only 48 weeks — with the plateau still developing. The difference is likely driven by the glucagon receptor agonism in retatrutide, which adds thermogenesis on top of the appetite suppression and insulin effects shared by both drugs. Tirzepatide is FDA approved; retatrutide is investigational.
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