Retatrutide: about 24–25% weight loss at 80 weeks in obesity without diabetes

Design

Phase 3, randomised, double-blind, placebo-controlled, 80 weeks

Population

2339 adults with obesity without diabetes

Primary outcome

Percent change in body weight (9 mg and 12 mg vs placebo)

Effect

−23.7% (9 mg) and −25.0% (12 mg) vs −3.9%; differences −19.8 and −21.0 points

TRIUMPH-1 was a phase 3, double-blind trial in 2339 adults with obesity but without diabetes, randomised to weekly subcutaneous retatrutide 4 mg, 9 mg or 12 mg, or placebo, for 80 weeks. Retatrutide acts on three receptors at once: GIP, GLP-1 and glucagon.

Mean weight change was −17.6%, −23.7% and −25.0% across the three doses, against −3.9% with placebo. The placebo-adjusted differences for the two higher doses were about 20 and 21 percentage points. In the 574 participants with knee osteoarthritis, pain scores fell more than with placebo, by about 1.6–1.8 points on a 10-point scale. In the 243 with obstructive sleep apnoea, the apnoea–hypopnoea index fell by about 22–25 more events per hour than placebo.

The size of the weight effect is larger than reported for current GLP-1 and dual agonists in comparable trials, though no head-to-head comparison has been made. Gastrointestinal effects were the most common adverse events, and the abstract does not give discontinuation rates.

For now this is an investigational drug. It changes the conversation about where obesity pharmacotherapy is heading, not what to prescribe this week.

• Retatrutide is investigational; patients asking for it cannot be prescribed it outside trials at present.
• Expect gastrointestinal effects to be the main tolerability issue, as with existing incretin drugs.
• In patients with knee osteoarthritis or sleep apnoea, weight loss of this scale brought measurable symptom gains in the trial.
• The trial excluded people with diabetes; separate trials are needed before applying these figures to type 2 diabetes.

Why it matters

Pharmacological weight loss is approaching the range once seen only after bariatric surgery.

Don't overread it

There is no head-to-head comparison with tirzepatide or semaglutide, and long-term outcomes are not yet reported.

The statistics, in plain English

A placebo-adjusted difference of about 21 percentage points means that, on average, a 100 kg person on 12 mg lost about 21 kg more than on placebo. The P<0.001 values say chance is very unlikely to explain this, but do not show how individual responses varied.

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