Retatrutide, called "reta" or the "reta peptide" in the research community, is a synthetic peptide that activates three hormone receptors at once: GLP-1, GIP, and glucagon. Eli Lilly is developing it through the Phase 3 TRIUMPH program. Four Phase 3 trials have reported, with average weight loss from 20.8% in type 2 diabetes up to 28.7% at 68 weeks in obesity with knee osteoarthritis, and 30.3% in a 104-week extension. Lilly plans to file a Biologics License Application in Q1 2027. It is not approved anywhere today.
Research notes
How does Retatrutide work?
Retatrutide — shortened to "reta" or the "reta peptide" in forums and vendor listings — is a synthetic peptide that activates three distinct hormone receptors at once: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon. The combination is what makes it different from tirzepatide (dual GLP-1 / GIP) and semaglutide (GLP-1 only).
The third agonism — glucagon — is the source of both the larger weight-loss effect observed in trials and the metabolic side-effect profile that's still being characterized in Phase 3.
What doses are used in research?
Phase 2 studies escalated from 1 mg weekly through 12 mg weekly over 24 weeks. The dose-response curve in published data is roughly linear through 8 mg, with diminishing returns above. Half-life of approximately six days supports weekly dosing. The full published titration schedule - 2 mg to 12 mg weekly with roughly four-week steps - is broken down in our retatrutide dosing protocols read.
What does this guide cover?
Vendor audits for retatrutide focus on COA-verified purity and identity, since the molecule is novel enough that some grey-market vendors have shipped under-purity or misidentified material in early 2026. Whether a vendor's retatrutide certificate can be checked against the issuing lab's own record weighs most in our COA score for this compound. One identity wrinkle specific to retatrutide: several vendors sell it under house labels such as GLP-3 RT rather than its real name. It is the same molecule (CAS 2381089-83-2) — the relabel just makes price comparison and identity checks harder. We decode it in GLP-3 RT is retatrutide. Whether research vials hold retatrutide at all is answered from 323 public lab results in does research retatrutide contain retatrutide.
Related reading
- GLP-3 RT is retatrutide: decoding the relabel
- Where to buy retatrutide in 2026
- Retatrutide vs tirzepatide
- Retatrutide dosing protocols: the TRIUMPH step-up chart
What did the Phase 3 trials show?
Four TRIUMPH trials have reported top-line results.
| Trial | Population | Duration | Weight loss at 12 mg | Reported |
|---|---|---|---|---|
| TRIUMPH-4 | obesity + knee osteoarthritis | 68 weeks | 28.7% (71.2 lbs) | Dec 2025 |
| TRIUMPH-1 | obesity, no diabetes | 80 weeks | 28.3% (70.3 lbs) | May 2026 |
| TRIUMPH-2 | type 2 diabetes + obesity | 80 weeks | 20.8% (49.6 lbs) | Jul 2026 |
| TRIUMPH-3 | severe obesity + established CVD | 80 weeks | 22.6% (55.8 lbs) | Jul 2026 |
A 104-week extension of TRIUMPH-1 reached 30.3% in participants with BMI of 35 or above. The gap between the diabetes and non-diabetes populations, 20.8% against 28.3% at the same dose and duration, matches the pattern seen with other incretin drugs.
The trade-off is tolerability. Discontinuation from adverse events in TRIUMPH-1 ran 4.1% at 4 mg, 6.9% at 9 mg and 11.3% at 12 mg, against 4.9% on placebo. Full detail is in our retatrutide Phase 3 results.
Related reading
- Retatrutide Phase 3 results - all four TRIUMPH readouts and the Q1 2027 filing plan.
- Retatrutide dosing protocols - the published titration ladder.
- Retatrutide side effects - the reported adverse-event profile.
- Retatrutide vs tirzepatide - why the cross-trial comparison is unreliable.
- Where to buy retatrutide - the research-market picture and what to verify.
- UBT251 vs retatrutide - the Novo-licensed triple agonist Reddit calls its successor, and what the trials show.
What it's researched for
- weight loss
- metabolic dysfunction
- fatty liver
Where to source it
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Frequently asked about Retatrutide
What is retatrutide?
Retatrutide is a synthetic peptide developed by Eli Lilly that activates three distinct hormone receptors at once: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon. It is in the company's Phase 3 TRIUMPH trial program for obesity and related metabolic indications.
What is the "reta peptide"?
"Reta" and "reta peptide" are the community shorthand for retatrutide, the same Eli Lilly triple-agonist (CAS 2381089-83-2). The nickname shows up in forums and in vendor listings, sometimes alongside house labels like "GLP-3 RT". It refers to the same molecule described on this page; there is no separate compound called reta.
What are the side effects of reta (retatrutide)?
In Lilly's Phase 3 TRIUMPH trials the most common adverse events were gastrointestinal — nausea, diarrhea and vomiting — and they rose with dose. Discontinuation from adverse events reached 11.3% at the 12 mg dose in TRIUMPH-1 against 4.9% on placebo. These are trial figures for pharmaceutical-grade material under medical supervision; they are not a safety profile for unregulated research-grade vials, whose purity and content vary. This is trial data, not human-use guidance.
How is retatrutide different from tirzepatide?
Tirzepatide is a dual agonist (GLP-1 and GIP). Retatrutide adds a third agonism — glucagon — which is the source of both the larger weight-loss effect observed in trials and the metabolic side-effect profile that's still being characterized in Phase 3.
Is retatrutide FDA-approved?
No. Four Phase 3 TRIUMPH trials reported between December 2025 and July 2026, and Eli Lilly stated on 23 July 2026 that it plans to submit a Biologics License Application to the FDA in Q1 2027. A standard review would place a decision in late 2027 or 2028. Anyone selling retatrutide today is selling unregulated research-grade material, not a prescription medication.
What doses are used in retatrutide research?
The Phase 3 TRIUMPH trials used 4 mg, 9 mg and 12 mg weekly subcutaneous after titration. Earlier Phase 2 dose-escalation (NEJM, 2023) tested 1, 4, 8 and 12 mg. Half-life is approximately 6 days, consistent with once-weekly dosing. Discontinuation from adverse events rose with dose, reaching 11.3% at 12 mg in TRIUMPH-1 against 4.9% on placebo.
What is the typical purity of research-grade retatrutide?
Janoshik Analytical's public data, 68 retatrutide reports to 30 June 2026, shows a median HPLC purity of 99.78% and a minimum of 99.04%, with identity confirmed on all 68 ([Janoshik retatrutide and tirzepatide results](/articles/janoshik-tirzepatide-retatrutide-results)). Measured content varies far more than purity. Per-vendor purity and any flagged lots are visible in the leaderboard on this page.