Retatrutide (LY3437943) is an investigational drug from Eli Lilly that activates three hormone receptors: GIP, GLP-1 and glucagon. As of October 7, 2026 it is not approved by FDA or any other regulator. Lilly has reported results from five phase 3 trials and says it plans to submit retatrutide for US approval in the first quarter of 2027. Vials sold online as "research" retatrutide are a different thing entirely: unregulated chemicals with no approval behind them.
Notice: Research peptides are sold for in-vitro laboratory research only. They are not FDA-approved, not for human or animal consumption, and this page is not medical advice. It contains no dosing or use guidance. We summarize public trial and regulatory documents and don't test products ourselves.
Mechanism class: a "triple agonist"
Approved drugs in this family act on one or two receptors. Semaglutide targets GLP-1; tirzepatide targets GIP and GLP-1 (compared in semaglutide vs tirzepatide). Retatrutide adds a third, the glucagon receptor. Lilly describes it as "an investigational once-weekly triple hormone receptor agonist" (Lilly, September 30, 2026). That's why it's often called a "triple agonist" and, in the gray market, "GLP-3."
Who develops it
Eli Lilly discovered and is developing retatrutide under the code LY3437943. According to Lilly's explainer, phase 3 trials cover obesity, type 2 diabetes, knee osteoarthritis pain, obstructive sleep apnea, chronic low back pain, cardiovascular and kidney outcomes, and MASLD (a form of fatty liver disease).
What the trials have reported
The evidence sits at different stages. Peer-reviewed papers carry more weight than company press releases, which are topline summaries. We list each source so you can check it.
Phase 2 (NEJM, June 2023)
A 48-week, randomized, placebo-controlled trial of 338 adults with obesity or overweight, without type 2 diabetes (Lilly; Jastreboff et al., NEJM). The primary endpoint was percent change in body weight at 24 weeks.
- 24 weeks: -17.5% in the highest dose group vs -1.6% on placebo
- 48 weeks: -24.2% in the highest dose group vs -2.1% on placebo
(Figures as reported by Hospital Pharmacy Europe, summarizing the paper.)
Phase 3: the TRIUMPH and TRANSCEND programs
| Trial | Population | Length | Primary result reported | Source |
|---|---|---|---|---|
| TRIUMPH-4 | Obesity with knee osteoarthritis | 68 weeks | Announced December 11, 2025 | Lilly |
| TRIUMPH-1 | Obesity or overweight, no diabetes (2,339 people) | 80 weeks | -19.0% to -28.3% body weight across dose groups vs -2.2% placebo | Lilly, May 21, 2026 |
| TRANSCEND-T2D-1 | Type 2 diabetes (537 people) | 40 weeks | A1C down up to 2.0 points from 7.9%; published in The Lancet | Lilly, June 6, 2026 |
| TRIUMPH-2 | Type 2 diabetes with obesity or overweight (1,152 people) | 80 weeks | -12.7% to -20.8% vs -4.0% placebo | Lilly, July 23, 2026 |
| TRIUMPH-3 | Severe obesity with cardiovascular disease (1,949 people) | 80 weeks | -21.6% to -22.6% vs -3.2% placebo | Lilly, July 23, 2026 |
TRIUMPH-1 also included nested sub-studies in knee osteoarthritis pain and obstructive sleep apnea, and Lilly reported results for both (Lilly, June 6, 2026). Phase 3 results were presented at the EASD meeting in Milan on September 30, 2026 (Lilly). NEJM lists a paper titled "Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity," but the journal blocked our access, so we couldn't confirm which trial it reports or its date.
Side effects
Gastrointestinal events (nausea, diarrhea, constipation, vomiting) were the most common in every trial, and dysesthesia, an abnormal skin sensation, was reported more often than on placebo. Discontinuation for adverse events reached 18.2% in one TRIUMPH-4 dose group. The full breakdown is in retatrutide side effects.
Regulatory status (October 2026)
- Not approved. Lilly "plans to subsequently submit retatrutide in Q1 2027 for U.S. approval," after completing the manufacturing (CMC) data package (Lilly, July 23, 2026). Lilly says "No medicine containing retatrutide has yet been approved for human use by any regulatory agency in the world" (Lilly, August 12, 2026).
- Not compoundable. FDA's GLP-1 page, current as of October 1, 2026, states: "Retatrutide and cagrilintide cannot be used in compounding under federal law" (FDA).
- "Research" labels don't help sellers. The same FDA page says it warned companies selling unapproved drugs "falsely labeled 'for research purposes' or 'not for human consumption.'" In the August 24, 2026 Peptide Partners letter, FDA identified a product called "GLP-3 Reta" as retatrutide. More in FDA peptide regulation in 2026.
- Lilly is suing sellers. On August 12, 2026, Lilly announced six new lawsuits against US entities selling "black-market" retatrutide and said it had reported more than 14,000 websites, ads, posts and listings (Lilly).
Why a research-labeled vial isn't the trial drug
The trial results above describe Lilly's product, made under drug manufacturing controls and given under trial protocols. A vial sold as research retatrutide has none of that behind it:
- No regulator checks it. Its identity, purity and fill depend on the seller and whatever lab it uses.
- Its contents can differ. Lilly warns that illicit products "may contain unknown ingredients, harmful contaminants and impurities" or the wrong amount of active ingredient (Lilly).
- Code names hide what's sold. Vendors often list it as "GLP-3," "RT" or similar. We count code-named listings against a vendor's transparency, and FDA has shown it will identify them anyway.
- None of the trial data transfers. Results from a clinical program say nothing about a gray-market vial.
How to check a retatrutide COA
Independent data shows why this matters. Finnrick lists 4,367 retatrutide tests across 378 vendors, from December 17, 2024 to September 25, 2026, graded against its default "purity 99.5%+, dose ±35%" standard. Results vary widely by vendor. Use our COA guide and check:
- The compound is named as retatrutide. A COA for "GLP-3" or a code doesn't tell you what was tested.
- Identity by mass spectrometry, not just HPLC purity. Purity alone can describe the wrong molecule.
- Measured net content vs the label. Retatrutide is sold in many vial sizes; quantity checks catch underfills.
- A lot number matching your vial, and a recent test date.
- A named lab you can verify. Janoshik has a verify page (task number plus key), and Freedom Diagnostics has an accession-number search.
- The vendor's Finnrick page and FDA record (warning letters).
For example, the PSPeptides retatrutide certificate we opened names the compound, a lab (North American Diagnostics), a batch number and a method, but no accreditation or verification key (review).
Which vendors we rate sell it
Several vendors we rate list retatrutide, some under its name and some under codes. We compare their COAs, labs and prices, for research use only, in best retatrutide vendors. Our method and overall list are at best peptide vendors in the USA.
Sources are linked inline and were checked October 7, 2026. We'll update this page when Lilly files with FDA or more TRIUMPH papers are published.