Retatrutide: what the trials have shown so far

Retatrutide is Eli Lilly's once-weekly injected triple agonist: it acts on the GLP-1, GIP and glucagon receptors. Tirzepatide acts on the first two. The glucagon arm is thought to raise energy expenditure and pull fat out of the liver. Retatrutide is not approved by the FDA, the EMA or any other regulator. In July 2026 Lilly said it plans to submit it to the FDA in the first quarter of 2027. Everything on this page is trial data, and some of it is still only in press releases. The retatrutide compound page covers the molecule.

Phase 2: obesity (NEJM, 2023)

The trial that made retatrutide famous randomised 338 adults with obesity, or overweight with a weight-related condition, to placebo or one of several retatrutide doses for 48 weeks. At 24 weeks, the primary endpoint, weight fell 17.5 percent on 12 mg against 1.6 percent on placebo. At 48 weeks it fell 24.2 percent on 12 mg, 22.8 percent on the combined 8 mg groups and 17.1 percent on 4 mg, against 2.1 percent on placebo. On 12 mg, 100 percent lost at least 5 percent of body weight and 83 percent lost at least 15 percent. Gastrointestinal side effects were dose related and eased with a lower 2 mg starting dose. Heart rate rose with dose, peaked at 24 weeks and then declined.

Phase 2: type 2 diabetes (Lancet, 2023)

This trial randomised 281 adults with type 2 diabetes to placebo, dulaglutide 1.5 mg or retatrutide at doses from 0.5 to 12 mg for 36 weeks. At 24 weeks HbA1c fell 2.02 percentage points on retatrutide 12 mg, against 0.01 on placebo and 1.41 on dulaglutide. At 36 weeks weight fell 16.94 percent on 12 mg against 3.00 percent on placebo and 2.02 percent on dulaglutide. Gastrointestinal events were reported by 35 percent across the retatrutide groups, the same rate as on dulaglutide. There was no severe hypoglycaemia.

Phase 2a: liver fat (Nature Medicine, 2024)

A substudy of the obesity trial took 98 participants with metabolic dysfunction-associated steatotic liver disease (MASLD) and at least 10 percent liver fat on MRI. At 24 weeks, liver fat fell by a relative 82.4 percent on 12 mg and 81.4 percent on 8 mg, against a 0.3 percent rise on placebo. Liver fat returned to the normal range (below 5 percent) in 86 percent of people on 12 mg and none on placebo. Liver fat is an imaging measure, not a biopsy outcome; trials of liver scarring are a separate step. The fatty liver research page has the context.

Phase 3: TRIUMPH-1 (NEJM, September 2026)

TRIUMPH-1 randomised 2,339 adults with obesity and without diabetes to retatrutide 4, 9 or 12 mg or placebo for 80 weeks. Under the treatment-regimen estimand, which counts everyone randomised whether or not they stayed on the drug, weight fell 17.6 percent on 4 mg, 23.7 percent on 9 mg and 25.0 percent on 12 mg, against 3.9 percent on placebo.

When Lilly announced the result on 21 May 2026, the headline was 28.3 percent on 12 mg. That is the efficacy estimand, which estimates the effect had everyone stayed on the drug; on that basis placebo was 2.2 percent. Both numbers are correct. They answer different questions, and the 25.0 percent figure is the one comparable with how most trials report their primary result. In the press release, 11.3 percent stopped 12 mg because of adverse events, against 4.9 percent on placebo.

TRIUMPH-1 also had two subgroups. In 574 people with knee osteoarthritis, the WOMAC pain score improved by 3.5 and 3.6 points on 9 and 12 mg against 1.9 on placebo (hybrid estimand). In 243 people with obstructive sleep apnoea, the apnoea-hypopnoea index fell by about 32 to 34 events per hour against 9.9 on placebo. The sleep apnoea research page covers the drug class.

Phase 3: TRIUMPH-2 and TRANSCEND-T2D-1 (Lancet, 2026)

TRIUMPH-2 randomised 1,152 adults with obesity or overweight and type 2 diabetes. At 80 weeks, under the treatment-regimen estimand, weight fell 11.9 percent on 4 mg, 16.8 percent on 9 mg and 18.8 percent on 12 mg against 5.1 percent on placebo. As with every incretin drug, people with diabetes lost less than those without. Diarrhoea affected 34 percent on 12 mg against 13 percent on placebo, and nausea 28 percent against 8 percent. Two less familiar effects were more common on retatrutide: low blood pressure (6 percent on 12 mg against under 1 percent) and dysaesthesia, an abnormal skin sensation (7 percent against 1 percent). Stopping for adverse events was 8 percent on 12 mg and 12 percent on 9 mg, against 5 percent on placebo.

TRANSCEND-T2D-1 tested retatrutide alone in 537 adults with type 2 diabetes managed on diet and exercise. Over 40 weeks HbA1c fell 1.94 percentage points on 12 mg against 0.81 on placebo, and weight fell 15.3 percent against 2.6 percent.

Press releases not yet in journals

Two phase 3 results are, as of October 2026, known only from Lilly's announcements. TRIUMPH-4, reported in December 2025, studied adults with obesity and knee osteoarthritis for 68 weeks: 28.7 percent weight loss on 12 mg against 2.1 percent on placebo, using the efficacy estimand, with large falls in knee pain. TRIUMPH-3, reported in July 2026, enrolled 1,949 adults with a BMI of 35 or more and established cardiovascular disease: 22.6 percent on 12 mg against 3.2 percent on placebo at 80 weeks. Press-release figures have not been through peer review, and the estimand is not always stated.

What is not known yet

No cardiovascular outcomes result. No data beyond 80 weeks. No head-to-head trial against tirzepatide. Rare side effects only show up in larger, longer use. The approved dose ladder, warnings and label will come with any approval. Retatrutide obtained outside a trial is not an approved product, and nothing on this page tells you what is in such a vial. Compare with the approved drugs on GLP-1 clinical trials and the SURMOUNT trials.

Logging it

If you are in a trial, the trial team holds the record, and a personal log of weekly dose, weight, heart rate and side effects is a useful copy. Peptide AI lists retatrutide in its library and keeps dose, weight, side effects and labs on one timeline, with logging free. It does not sell or source the drug. See the retatrutide tracker or the free GLP-1 tracker.