What is retatrutide? Benefits, evidence and what independent lab tests show

Retatrutide is an investigational peptide, developed by Eli Lilly, that activates three separate hormone receptors at once — GIP, GLP-1, and glucagon — to drive weight loss and improve blood sugar. It is not approved by the FDA or any other regulatory agency. Lilly's own FAQ is direct about this: retatrutide "is not currently approved by the FDA and is considered an investigational medication," legally available "only through Lilly's clinical trials," and "anything sold to consumers outside of those trials is illegal, with no way to verify its safety, purity or dosing" (Eli Lilly, "What to know about retatrutide"). Since August 3, 2026, Lilly has also run a limited pre-approval expanded-access program for eligible patients through their doctors (ClinicalTrials.gov NCT07629401); it does not sell retatrutide to consumers. It's sold anyway, labeled "for research use only," through the same market that sells tirzepatide and other compounds outside the pharmacy system — which is what most of this article, and our database, actually covers.

What retatrutide is and how it works

Retatrutide is a single synthetic peptide, chemically identified as LY3437943, engineered to activate three separate receptors: GIP, GLP-1, and glucagon. That's one more target than tirzepatide (which hits two) and two more than semaglutide (which hits one), and it's why buyers sometimes call retatrutide "GLP-3" — an informal nickname, not a real drug class. Lilly's own FAQ addresses this directly: "'GLP-3' is a scientifically inaccurate label used informally in the media... this nickname emerged because the medication simultaneously targets three receptors... rather than representing an actual scientific classification. A more suitable term... is 'triple agonist.'" Its developer is Eli Lilly (Lilly retatrutide FAQ).

Where retatrutide stands today: it has completed a published Phase 2 trial and has moved into a Phase 3 program (called TRIUMPH for obesity-related studies and TRANSCEND-T2D for diabetes) that Lilly has begun reporting topline results from, but as of this writing it has not been approved by the FDA or any other regulator, and there is no brand name yet. Lilly said on July 23, 2026 that it plans to submit a Biologics License Application to the FDA in the first quarter of 2027 (Eli Lilly announcement, July 23, 2026). That's a meaningfully different status than tirzepatide or semaglutide, both of which are approved, branded drugs — treat any claim that retatrutide is "the new Ozempic" or already available by prescription with real skepticism.

What people use it for

What the research actually shows

Weight loss in the published Phase 2 trial

The first retatrutide trial published in a peer-reviewed journal was a phase 2, double-blind, randomized, placebo-controlled trial of 338 adults with a BMI of 30 or higher (or 27 to 30 with a weight-related condition), none of whom had diabetes. Participants received one of several retatrutide dose regimens or placebo for 48 weeks. At the highest dose studied, the average body-weight reduction was 17.5% at 24 weeks and 24.2% at 48 weeks, compared with 1.6% and 2.1% on placebo at the same points. At 48 weeks, every participant on the highest dose studied had lost 5% or more of their body weight, 93% had lost 10% or more, and 83% had lost 15% or more (Jastreboff et al., NEJM 2023). That's a larger effect, in this one trial, than the SURMOUNT-1 result for tirzepatide reported around the same period — though the trials weren't run head-to-head, so a direct comparison isn't something this data can support.

Phase 3: the first peer-reviewed results

Two Phase 3 trials have now been published in The Lancet, both funded by Lilly. TRANSCEND-T2D-1 randomized 537 adults with type 2 diabetes not controlled by diet and exercise to retatrutide or placebo for 40 weeks; at week 40 the highest dose studied cut HbA1c by 1.94 percentage points versus 0.81 on placebo and body weight by 15.3% versus 2.6% (treatment-regimen estimand), and the most frequent side effects were mostly mild to moderate gastrointestinal events (Bajaj et al., The Lancet, 2026). TRIUMPH-2 randomized 1,152 adults with obesity and type 2 diabetes for 80 weeks, and at week 80 the highest dose studied produced an average weight change of -18.8% versus -5.1% on placebo (treatment-regimen estimand); the most frequently reported side effects were gastrointestinal, including diarrhea in 34% versus 13% on placebo (Bellido et al., The Lancet, 2026).

Other TRIUMPH trials, including ones that looked at knee osteoarthritis pain and sleep apnea, have been reported by Lilly in press releases but not yet, as far as we could find, as full peer-reviewed papers; studies of heart, kidney and fatty liver outcomes are ongoing (Lilly retatrutide FAQ). A trial comparing retatrutide directly with tirzepatide (TRIUMPH-5) is under way, with no results posted yet (ClinicalTrials.gov NCT06662383). Our tirzepatide vs retatrutide comparison covers what can and can't be compared today.

Safety signals from the Phase 2 trial

In the published Phase 2 trial, the most common adverse events in the retatrutide groups were gastrointestinal — consistent with the pattern seen in tirzepatide and semaglutide trials — and were described as dose-related, mostly mild to moderate, and partially reduced when treatment started at a lower initial dose rather than a higher one. The trial also noted dose-dependent increases in heart rate that peaked partway through the trial and declined afterward. The trial was funded by Eli Lilly (Jastreboff et al., NEJM 2023).

Why retatrutide draws so much buyer interest before it's even approved

It's worth asking why a drug that isn't approved anywhere is already the second most-tested compound in our database. Part of the answer is straightforward publicity: a triple-receptor mechanism, a headline 24.2% average weight loss in its Phase 2 trial (a different trial from tirzepatide's, so not a like-for-like comparison), and years of Lilly press coverage as the Phase 3 program has progressed. None of that publicity changes retatrutide's regulatory status — a molecule can generate enormous buyer demand for its research-labeled version years before, or instead of, ever reaching a pharmacy. That gap between attention and availability is exactly the space the grey market fills, and it's why independent lab data matters more here than for a drug buyers could otherwise just get from a pharmacist.

Side effects and risks

Because retatrutide isn't approved, there's no FDA label and no boxed warning to point to — which cuts both ways. It means there's no long-term, large-scale safety database like the one behind Mounjaro or Ozempic; the longest published trial so far ran 80 weeks in about 1,150 people, far short of the years of data behind approved drugs. It also means claims that retatrutide is "safer" or "gentler" than approved drugs aren't something the current evidence can support one way or the other. Lilly's own FAQ is blunt about the products actually sold under this name outside its trials: "Illicit retatrutide products may contain unknown ingredients, harmful contaminants and impurities. These products may also have too much or too little active ingredient, or the wrong ingredient entirely." That's the manufacturer of the real molecule describing what's being sold in its name — not us.

What the lab tests show

As of September 30, 2026, our database includes 341 retatrutide vials from 37 vendors, drawn from 193 lab reports dated October 2024 through September 2026. As of September 29, 2026, the reports then on file came from 12 labs, and retatrutide was the second most-tested compound we track, behind tirzepatide. Purity is generally strong: 341 vials have a purity result, and 322 of them (94%) came in at 99% or higher, with a median of 99.70%. 7 vials tested under 95% purity, and every one of those counts as a failure under our scoring rules.

Dose against label shows more spread. Across 295 vials with both a label amount and a measured amount, the median result ran 8.2% over label. 94 of those vials (32%) landed within ±5% of label; as of September 29, 2026, 167 of 292 (57%) landed within ±10%. At the tails, 6 vials measured more than 20% under label, and 30 measured more than 20% over, with 1 more than 50% over. As of September 29, 2026, no vial in our retatrutide data had been reported empty. Altogether, 14 of the 341 tested vials (4.1%) counted as a failure. As of September 29, 2026, the 14 failures were spread across 9 of the 37 vendors, with no more than 3 at any single one — 28 of the 37 vendors had no failed retatrutide vial on file. Overfill wasn't spread evenly across vial sizes or years: it ran highest among smaller vial sizes and was worse in reports from 2025 than in 2026, when a larger share of vials landed within ±5% of label.

Add-on testing is less common for retatrutide than the core purity and quantity checks. Of 61 endotoxin results, 24 came back below the lab's detection limit and most of the rest clustered at the lower end of the reported range, though a handful ran considerably higher and units aren't always reported consistently between labs. Sterility testing is rarer still — just 7 retatrutide samples checked for total aerobic microbial count and total yeast/mold count — and all 7 failed at least one of the two counts. That's a tiny, likely self-selected sample, probably skewed toward vials someone already suspected were a problem, and a failed microbial count on a sample prepared for lab testing is a finding about that sample, not a diagnosis about a person. It's still a real pattern in the data we have.

As of September 29, 2026, 9 of the 37 vendors with retatrutide results have enough reports (five or more) to be ranked specifically on this compound. Here's the live picture, which updates as new reports come in:

For the full breakdown by vial size and by year, see the retatrutide results page, which stays current, and our companion article, retatrutide test results: what 336 lab-tested vials show; can you buy retatrutide in the USA? covers the legal picture in more depth.

What the data can't tell you

A lab report on a retatrutide vial can tell you what's actually in it, at what purity and what amount relative to the label. It can't tell you whether the trial data above — all of it from Lilly's own controlled studies — translates the same way to a research-labeled product made by an unrelated, unknown manufacturer; a lab report confirms the molecule's presence and amount, not that the manufacturing process behind it matches anything Lilly does in an FDA-regulated facility. It also can't tell you anything about a vendor's shipping speed, communication, or how it handles a bad result — those aren't things a chemistry test measures.

Buying smarter

Because retatrutide isn't approved anywhere, there's no pharmacy version to compare against — every vial on the research market is unregulated by definition, so the checks that matter are the same ones that matter for any research peptide. Check a vendor's specific retatrutide record at /peptides/retatrutide rather than its overall reputation. Learn to read a peptide COA and watch for fake-COA red flags before trusting anything a vendor posts. Given how thin the endotoxin and sterility data is for this specific compound, an independent lab test on your own vial is worth more here than for a compound with a deeper testing history. If a report comes back bad, stop using that batch, tell anyone who bought from the same run, bring it to the vendor, and submit it to VendorVerify.

Quotes are from Eli Lilly's "What to know about retatrutide" FAQ, and from Jastreboff et al., New England Journal of Medicine, 2023. Database figures without a date update automatically from VendorVerify's lab results; dated figures are snapshots. This isn't medical or legal advice, and research-labeled retatrutide is sold for research use only.