Retatrutide phase 3 results so far: one peer-reviewed trial and four company-reported TRIUMPH readouts

TRANSCEND-T2D-1 was a 40-week, double-blind, placebo-controlled phase 3 trial at 48 sites in the USA, Mexico and India. It randomised 537 adults with type 2 diabetes that diet and exercise alone were not controlling. Participants received retatrutide 4 mg, 9 mg or 12 mg, or placebo, by once-weekly injection under the skin ^[1]. The paper appeared online in The Lancet on 6 June 2026, and the registry lists the trial as completed ^[2].

The primary end point was the change in HbA1c at week 40. For the treatment-regimen estimand, HbA1c fell by 1.69, 1.86 and 1.94 percentage points on the three doses, against 0.81 on placebo. Body weight, a key secondary end point, fell by 11.5%, 13.9% and 15.3%, against 2.6% on placebo ^[1].

The most frequent adverse events were gastrointestinal, generally mild to moderate, and subsided over time. Between 2% and 5% of people on retatrutide stopped treatment because of adverse events, against none on placebo. No severe hypoglycaemia was reported. Two deaths occurred, both in the 4 mg group, and the authors judged both unrelated to the drug ^[1].

TRIUMPH is Lilly's registration programme for obesity. A design paper describes four phase 3, double-blind, placebo-controlled trials in more than 5,800 participants, with sleep apnoea and knee osteoarthritis studies nested inside the main weight trials ^[3]. None of the TRIUMPH results had appeared in a peer-reviewed journal when we checked in September 2026, so the figures below are the company's own.

The first TRIUMPH readout came on 11 December 2025. In TRIUMPH-4, in adults with obesity or overweight and knee osteoarthritis, Lilly reported 68-week weight loss of 26.4% on 9 mg and 28.7% on 12 mg against 2.1% on placebo (efficacy estimand), and falls in the WOMAC knee pain score of 4.5 and 4.4 points against 2.4 points on placebo, from an average baseline of 6.0 ^[8].

On 21 May 2026, Lilly reported topline results from TRIUMPH-1, which randomised 2,339 adults with obesity, or overweight with at least one weight-related condition, and without diabetes, to retatrutide 4 mg, 9 mg or 12 mg or placebo for 80 weeks. The headline retatrutide weight loss results were 19.0%, 25.9% and 28.3% on the three doses against 2.2% on placebo, using the efficacy estimand, which assumes people stay on treatment. Using the treatment-regimen estimand, the figures were 17.6%, 23.7% and 25.0% against 3.9% ^[4].

Lilly reported nausea in 28.6% to 42.4% of people on retatrutide against 14.8% on placebo, and dysesthesia, an altered or unpleasant skin sensation, in 5.1% to 12.5% against 0.9%. Discontinuation because of adverse events was 4.1%, 6.9% and 11.3% on the three doses against 4.9% on placebo ^[4].

On 23 July 2026, Lilly reported that TRIUMPH-2 and TRIUMPH-3 had met their primary end points. In TRIUMPH-2, in adults with obesity or overweight and type 2 diabetes, Lilly reported 80-week weight loss of 12.7%, 19.1% and 20.8% on 4 mg, 9 mg and 12 mg, against 4.0% on placebo, with HbA1c reductions of up to 1.6 percentage points ^[5].

TRIUMPH-3 enrolled adults with severe obesity and established cardiovascular disease. Lilly reported weight loss of 21.6% on 9 mg and 22.6% on 12 mg, against 3.2% on placebo. Major cardiovascular events were fewer than expected in both arms, and the pre-specified comparisons did not show a clear difference: the hazard ratio for the five-part MACE composite was 0.82 (95% CI 0.55 to 1.22), and for the three-part composite 1.12 (0.64 to 1.96) ^[5]. Confidence intervals that cross 1 mean the trial cannot say whether retatrutide raised or lowered that risk.

Lilly reported discontinuation because of adverse events of up to 11.6% in TRIUMPH-2 and up to 13.5% in TRIUMPH-3 on retatrutide, against 4.9% and 4.8% on placebo ^[5]. In the same release, Lilly said it had the data package to support global submissions for obesity, knee osteoarthritis pain and obstructive sleep apnoea ^[5]. We have not found a regulator's confirmation of any filing, so we do not report a filing date.

The trial many readers wait for is TRIUMPH-5, a randomised, double-blind phase 3 study comparing retatrutide directly with tirzepatide in adults with obesity. On ClinicalTrials.gov its status is active, not recruiting, with about 800 participants, a primary completion date estimated for November 2026 and study completion estimated for December 2026. The record was last updated in July 2026 ^[6].

Until TRIUMPH-5 reports, any retatrutide vs tirzepatide claim rests on separate trials with different populations and durations. Our retatrutide vs tirzepatide comparison sets out what can and cannot be compared.

Retatrutide is not approved in the US. As of 1 September 2026, the FDA said it is not a component of any FDA-approved drug and cannot be used in compounding under federal law ^[7]. The same page says FDA has warned companies that sold retatrutide and other GLP-1 drugs falsely labelled "for research purposes" ^[7]. Our legal status guide covers the position by country, including the UK.

These retatrutide results come from people in monitored trials using Lilly's investigational product at the doses above. The side effects were recorded under that supervision, and the trials say nothing about the identity, purity or dose of products sold online. No FDA decision date has been published. Doses in this article are the trial doses only and are not guidance.