Research brief

Retatrutide

Also written as LY3437943, triple hormone receptor agonist

Evidence read from: ClinicalTrials.gov, PubMed, FDA, Company disclosures · how we work · Last reviewed 9 August 2026

This brief is different from the others in the library. Retatrutide has one of the strongest efficacy datasets ever assembled for an investigational obesity drug, published in the New England Journal of Medicine, The Lancet and Nature Medicine, with four completed phase 3 trials covering more than 5,800 people. It also cannot be lawfully prescribed anywhere on earth, and the closest thing to an analysis of the gray-market supply chain found that half the test purchases never arrived and every vial that did was a probable falsified product.

Marketed for

Weight loss.

Evidence reviewed

9 August 2026, against 21 sources

Human evidence

Graded, for members. See the membership

If you read nothing else

• •The phase 2 obesity trial randomized 338 people over 48 weeks and reported weight reduction from 8.7 percent at the lowest of four dose levels to 24.2 percent at the highest, against 2.1 percent on placebo.
• •Four phase 3 trials have completed, covering more than 5,800 people, with results up to about 28 percent weight reduction. None of the four has been peer reviewed or had results posted. They exist in the public record only as company press releases.
• •The tolerability cost rises with dose and duration. Discontinuation for adverse events was under 2 percent across the 48-week phase 2 trial, but 11.3 percent at the highest dose over 80 weeks in one phase 3 trial and 18.2 percent over 68 weeks in another.
• •The cardiovascular and kidney outcomes trial, 10,000 people, does not complete until February 2029. Nobody yet knows this drug’s effect on hard outcomes.
• •Retatrutide is approved by no regulator anywhere. The manufacturer stated in July 2026 that it plans to submit for US approval in the first quarter of 2027. The FDA has said in terms that it "cannot be used in compounding under federal law".
• •When researchers made six test purchases of a related drug from illegal online pharmacies, three orders never arrived. Every vial that did arrive was assessed as a probable falsified product, containing 28.6 to 38.7 percent more labeled active ingredient than stated, at a measured purity of 7.7 to 14.4 percent against a claimed 99 percent.

Five of the sources, and what they say

Open any of them. Each is tagged with the kind of evidence it is, because a randomized trial in people and an experiment in cell culture answer very different questions. This brief was written against 21 sources of this kind.

1. 1.Human RCT
   Jastreboff AM, Kaplan LM, Frias JP, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023;389(6):514-526. PMID 37366315. Open source
2. 2.Trial registry
   A study of LY3437943 in participants with obesity or overweight. ClinicalTrials.gov NCT04881760. Participant flow and discontinuation data posted. Open source
3. 3.Human RCT
   Rosenstock J, Frias J, Jastreboff AM, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial. Lancet. 2023;402(10401):529-544. PMID 37385280. Open source
4. 4.Human RCT
   Sanyal AJ, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease. Nat Med. 2024;30(7):2037-2048. PMID 38858523. Open source
5. 5.Human RCT
   Coskun T, Wu Q, Schloot NC, et al. Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2 randomised trial. Lancet Diabetes Endocrinol. 2025;13(8):674-684. PMID 40609566. 103 people with paired DXA scans. Open source

Members read on

The grade and the full review are for members

The findings above are free, and so are the sources. Behind this line is our grade for the human evidence on Retatrutide, the full review, what we looked for and could not find, and all 21 sources with the kind of evidence each one is.

The grade is our judgment, and the review is the working behind it: what has actually been run in people, what it measured instead, who ran it, who paid for it, and which results were never published at all. Our findings are above and our sources are open, so nothing here asks you to take the reasoning on trust. What a membership buys is where we land, and why.

Nobody who sells peptides pays us anything, and nothing we earn changes what a brief says. Members are the only people paying us, which is the only reason a brief here is free to be unflattering.

$5 a month or $29 a year. Membership opens in waves, so the button takes you to the place where you choose a price and hold a seat. No card is taken today. The peptide tracker stays free for everyone, member or not.