Retatrutide

Retatrutide is an investigational injectable that activates three receptors at once: GLP-1, GIP and glucagon. It is not approved by FDA for any use, and it is not available by prescription in the United States. Everything below comes from trial data, not from a label.

The phase 2 results are why it gets so much attention. Published in 2023, the trial enrolled 338 adults with obesity. At 48 weeks, average weight change was −8.7% at 1 mg, −17.1% at 4 mg, −22.8% at 8 mg and −24.2% at 12 mg, against −2.1% on placebo. At the 12 mg dose, 93% of participants lost at least 10% of body weight and 83% lost at least 15%. At the time, those were the largest figures published for a pharmacological weight treatment.

They also come with the usual caveats of an early trial. Phase 2 is smaller and shorter than phase 3, gastrointestinal adverse events were dose-related, and the trial recorded dose-dependent increases in heart rate that peaked at 24 weeks before declining. Phase 3 programs regularly produce smaller effects than phase 2 suggested.

Phase 3 results are now published. In TRIUMPH-1 (NEJM 2026), 2,339 adults with obesity but without diabetes were randomized to retatrutide 4, 9 or 12 mg or placebo; at 80 weeks, average weight change was −17.6%, −23.7% and −25.0% versus −3.9% on placebo (intention-to-treat). Lilly’s May 2026 press release cited a larger −28.3% at 12 mg, a figure that counts only people who stayed on treatment. In TRIUMPH-2 (Lancet 2026), 1,152 adults with obesity or overweight and type 2 diabetes lost 11.9%, 16.8% and 18.8% versus 5.1% on placebo at 80 weeks; gastrointestinal events were the most common side effects, and hypotension and dysesthesia (abnormal skin sensations) were more frequent than on placebo. Earlier, TRIUMPH-4 (Lilly topline, December 2025) reported 28.7% average weight loss at 12 mg in adults with obesity and knee osteoarthritis. Per Lilly, the company plans to submit a Biologics License Application to FDA in the first quarter of 2027.

The part that matters most for safety is regulatory, not clinical. FDA states plainly that retatrutide cannot be used in compounding under federal law, that it is not a component of any FDA-approved drug, and that it has not been found safe and effective for any condition. The agency has warned telehealth companies for marketing it, ingredient distributors for selling it to compounders, and outsourcing facilities for repackaging it. Anything sold online as retatrutide is outside the legal supply chain entirely.

If a provider offers you retatrutide today, the right question is what exactly they are selling and under what authority. Our retatrutide evidence review and mechanism comparison cover the trial record and the marketing around it.