Retatrutide Phase 3: The TRIUMPH Trial Results (2026)

When we covered retatrutide's Phase 2 trial, it ended with a single line: Phase 3 trials are ongoing as of 2026. Those trials — Eli Lilly's TRIUMPH programme — have now started to report, and the topline numbers are among the largest ever seen for a weight-loss compound. Here's a plain-English summary.

Important context: the figures below are topline results released by the manufacturer, with full peer-reviewed data expected at the American Diabetes Association 2026 Scientific Sessions. Retatrutide remains an investigational compound — it is not FDA-approved. Nothing here is medical advice, and Lotus Labs supplies retatrutide for research purposes only.

TRIUMPH-1: the pivotal obesity trial

TRIUMPH-1 randomised about 2,339 adults with obesity or overweight (without type 2 diabetes) to retatrutide 4 mg, 9 mg or 12 mg once weekly — each titrated up gradually — or placebo, over 80 weeks.

At the top 12 mg dose, mean body-weight reduction was approximately:

• ~25% under the conservative treatment-regimen estimand (which counts everyone as randomised, regardless of whether they stayed on treatment)
• ~28% under the efficacy estimand (participants who remained on treatment)

The lower doses followed a clear dose-response — roughly 24% at 9 mg and 18% at 4 mg — versus about 4% on placebo. In a longer 104-week extension, a subgroup with higher baseline BMI who escalated to their maximum tolerated dose reached up to ~30% average weight loss.

These two "estimand" figures explain why you'll see retatrutide quoted as both ~25% and ~28–30% depending on the source — they're measuring slightly different things, not contradicting each other.

TRIUMPH-4: obesity plus knee osteoarthritis

The programme's first Phase 3 readout (late 2025) studied adults with obesity and knee osteoarthritis. Participants lost close to 29% of body weight at 68 weeks, and the trial also reported reductions in knee pain and improvements in cardiovascular risk markers such as blood pressure and non-HDL cholesterol — suggesting benefits beyond weight alone.

Beyond obesity: type 2 diabetes

A separate diabetes-focused programme (TRANSCEND) reported a roughly 2.0-percentage-point drop in HbA1c alongside about 17% weight loss in people with type 2 diabetes, with data published in The Lancet in mid-2026.

How it compares

Retatrutide's Phase 3 numbers extend the pattern seen in Phase 2 (24.2% at 48 weeks):

The reason retatrutide reaches higher is mechanism: it's a triple agonist hitting GLP-1, GIP and glucagon receptors, where semaglutide hits one and tirzepatide two. Our GLP-1 comparison page lays the three side by side.

Safety

As in earlier trials, the most common adverse events were gastrointestinal (nausea, vomiting, diarrhoea), mostly during dose escalation, along with the modest heart-rate increase seen across the GLP-1 class. Full adverse-event tables will come with the peer-reviewed publications.

What's next

Lilly has said it expects several more Phase 3 readouts across the TRIUMPH programme through 2026, ahead of regulatory filings. Until any approval, retatrutide stays investigational.

If you're researching the triple agonist, see our retatrutide listings — Retatrutide 10mg and the pre-filled Retatrutide pen — or compare it against the other GLP-1s on the comparison page.

Lotus Labs supplies all products for research purposes only. This article summarises publicly reported trial data and is not medical advice.