Retatrutide: What It Is, Phase 3 Results and Where It Stands in 2026

What retatrutide is

The first two receptors, GIP and GLP-1, are also targeted by tirzepatide. Glucagon receptor activation is the third. Its effect in people is covered in retatrutide benefits, and the head to head with the approved dual agonist in retatrutide vs tirzepatide.

Phase 2 results by dose (NEJM, 2023)

The phase 2 trial (Jastreboff et al., NEJM 2023, NCT04881760) randomized 338 adults with obesity or overweight to weekly retatrutide or placebo for 48 weeks. Some arms started at 2 mg and some at 4 mg. The primary endpoint was the change in body weight at 24 weeks. Values are least-squares mean changes.

The authors report that gastrointestinal adverse events were dose related, mostly mild to moderate, and partly mitigated by starting at 2 mg rather than 4 mg, and that heart rate rose in a dose-dependent way, peaking at 24 weeks and declining after. Week by week curves are in retatrutide before and after; the dose schedule used is in the retatrutide dosage guide.

Phase 3 TRIUMPH and TRANSCEND results

All figures below are Lilly's topline or detailed releases and the linked papers. Lilly reports two estimands: the efficacy estimand (participants who stayed on treatment) and the treatment-regimen estimand (everyone randomized). The efficacy figures are larger. Dates are announcement dates.

Further points from the releases: in the TRIUMPH-1 extension for people with a baseline BMI of 35 or more, those who stayed on 12 mg lost an average of 30.3 percent at 104 weeks (532 participants entered the extension). In TRIUMPH-1 knee osteoarthritis and sleep apnea baskets, Lilly reported pain falling by up to 4.3 points on the 0 to 10 WOMAC scale and apnea severity by up to 36.1 events per hour. In TRIUMPH-3, cardiovascular events were fewer than expected in both arms and the hazard ratio for the five-part composite was 0.82 (95% CI 0.55 to 1.22), which does not show a difference. In every phase 3 trial, participants started at 2 mg weekly and stepped up every four weeks to the target dose.

Tolerability in TRIUMPH-1

Lilly said dysesthesia and urinary tract infections were generally mild to moderate and mostly resolved on treatment. Dose by dose detail is in retatrutide side effects.

What is still running

On ClinicalTrials.gov, TRIUMPH-5 compares retatrutide with tirzepatide in 800 adults with obesity, with a primary completion date of November 2026. The cardiovascular and kidney outcomes trial (NCT06383390, 10,000 participants) has a primary completion date of February 2029. TRIUMPH-6, -7, -8 and -9 are listed as active, not recruiting, with primary completion dates from 2027 to 2028. Registry dates move, so treat them as planned.

Approval, compounding and what FDA says

Lilly's own FAQ, last updated September 2026, says retatrutide is not yet available for public use and that no one should take anything claiming to be retatrutide outside a Lilly-sponsored trial. FDA's page on unapproved GLP-1 drugs (content current as of 1 October 2026) states: "Retatrutide and cagrilintide cannot be used in compounding under federal law." It adds that they are not components of FDA-approved drugs and have not been found safe and effective for any condition, and that FDA has warned telehealth companies, ingredient distributors and outsourcing facilities over retatrutide. FDA has also warned companies that sold semaglutide, tirzepatide, retatrutide, survodutide or mazdutide labelled "for research purposes" or "not for human consumption" directly to consumers with dosing instructions. For the incident record see black-market retatrutide: deaths and lawsuits, and for the legal route question compounded retatrutide.

Research vials

Peptide vendors list retatrutide as a laboratory reagent. It is unapproved, has no batch release or recall mechanism, and the seller's certificate is the only evidence of what is in the vial. Daily prices per mg are tracked in retatrutide cost and the sourcing picture in where to buy retatrutide. If you hold vials, mixing is in how to reconstitute retatrutide and general technique in how to reconstitute peptides.

Retatrutide pages on this site

For the wider field see tirzepatide dosage guide, semaglutide cost without insurance, mazdutide and peptides for weight loss.

Frequently Asked Questions

What is retatrutide?

Retatrutide (also called LY3437943) is an investigational once-weekly injection from Eli Lilly. A single molecule activates the receptors for GIP, GLP-1 and glucagon, which is why it is called a triple agonist. In clinical trials it is given as a weekly subcutaneous injection.

Is retatrutide FDA approved?

No. Lilly describes it as investigational and says it has not been approved by any regulatory agency. Lilly said on 23 July 2026 that it plans to submit a Biologics License Application to FDA in the first quarter of 2027, after completing its manufacturing data package.

How much weight did people lose on retatrutide in phase 3?

In TRIUMPH-1 (80 weeks, adults with obesity and no diabetes) the 4, 9 and 12 mg groups lost an average of 19.0, 25.9 and 28.3 percent of body weight on Lilly's efficacy estimand, against 2.2 percent on placebo. The New England Journal of Medicine paper reports the treatment-regimen estimand: 17.6, 23.7 and 25.0 percent against 3.9 percent on placebo.

Can retatrutide be compounded?

No. FDA states that retatrutide and cagrilintide cannot be used in compounding under federal law, that they are not components of FDA-approved drugs, and that they have not been found safe and effective for any condition. FDA has also warned companies selling these products labelled for research purposes or not for human consumption.

Where can I get retatrutide legally?

Lilly says retatrutide is legally available only to participants in its clinical trials. A single-patient expanded access program is also registered on ClinicalTrials.gov (NCT07629401) for adults with a BMI of 35 or more, at least two serious obesity-related complications, and no access to a trial. Requests come from the treating physician, not the patient.

What does GLP-3 mean?

Lilly calls it a scientifically inaccurate label used informally in the media for triple hormone receptor agonists such as retatrutide. It is not a drug class. The accurate term is triple agonist.

Sources

1. Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med 2023 (PMID 37366315)
2. Jastreboff AM et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1). N Engl J Med 2026 (PMID 42814954)
3. Bellido V et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2). Lancet 2026 (PMID 42810372)
4. Lilly, TRIUMPH-4 topline results, 11 December 2025
5. Lilly, TRANSCEND-T2D-1 topline results, 19 March 2026
6. Lilly, TRIUMPH-1 topline results, 21 May 2026
7. Lilly, TRIUMPH-1 and TRANSCEND-T2D-1 results at ADA, 6 June 2026
8. Lilly, TRIUMPH-2 and TRIUMPH-3 topline results and BLA plan, 23 July 2026
9. Lilly, TRIUMPH-2 detailed results, 29 September 2026
10. Lilly, What to know about retatrutide (FAQ, last updated September 2026)
11. FDA, FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss, content current 1 October 2026
12. ClinicalTrials.gov NCT07629401, pre-approval expanded access of retatrutide; registry entries for the TRIUMPH and TRANSCEND trials, read 27 October 2026