Lilly's retatrutide shows 26.6% placebo-adjusted weight loss in knee osteoarthritis trial
Eli Lilly's experimental retatrutide produced 26.6% placebo-adjusted weight loss at 68 weeks in people with obesity and knee osteoarthritis, but a nerve-related side effect appeared at higher rates.
Eli Lilly's investigational drug retatrutide produced 26.6% placebo-adjusted weight loss at 68 weeks in people who have obesity or are overweight and who also have knee osteoarthritis, according to Phase 3 TRIUMPH-4 results the company reported in December [1]. Analysts at BMO Capital Markets said at the time the results "help to solidify retatrutide's profile as an even higher efficacy next generation GLP-1+ asset" [1].
Retatrutide is a triple-G agonist, meaning it acts on three hormone receptors. Lilly has placed it in a "different drug category" from its current weight-loss medicines — the GLP-1/GIP dual agonist Zepbound (tirzepatide) and the pill Foundayo (orforglipron) — William Blair healthcare research analyst Andy Hsieh told BioSpace in an email [1]. Retatrutide is in Phase 3 testing and is not an approved medicine [1].
Lilly has reported larger weight-loss numbers elsewhere. In TRIUMPH-1, a Phase 3 trial in people with obesity but without diabetes, retatrutide generated 28.3% weight loss over 80 weeks, Lilly announced on May 21, likening the results to those seen with bariatric surgery [1]. Hsieh told BioSpace he expects the debate around retatrutide to center on the tradeoff between its weight-loss efficacy and its tolerability [1].
That tolerability question is tied to a specific safety signal. Lilly has reported a condition called dysesthesia — described as a neurological anomaly characterized by unpleasant or painful sensations — in more than a fifth of patients taking the 20-mg dose in TRIUMPH-4 [1]. Dysesthesia also appeared in TRIUMPH-1, with rates rising as the dose increased [1].
Why it matters for patients
TRIUMPH-4 was run in people who have both excess weight and knee osteoarthritis. The results reported so far cover weight loss only; whether participants' knee pain, joint function or other osteoarthritis measures changed has not been reported [1].
Retatrutide cannot be prescribed today. People taking an approved GLP-1 such as Ozempic, Wegovy or Rybelsus (semaglutide), Mounjaro or Zepbound (tirzepatide), or Foundayo (orforglipron) are using medicines that have cleared FDA review; retatrutide is still in late-stage testing [1].
The dysesthesia finding matters because it appeared in more than one trial and became more common at higher doses [1]. That pattern could affect how regulators and doctors weigh retatrutide's extra weight loss against side effects, though no regulatory decision or review timeline has been disclosed [1].
Competition is part of the picture. Novo Nordisk is developing CagriSema, a fixed-dose combination of semaglutide and the amylin analog cagrilintide, and its CEO said the company expects it on the U.S. market "early next year" at the time of a head-to-head readout reported in February [1]. In that REDEFINE-4 study, patients on CagriSema lost 23% of body weight on average at 84 weeks, compared with 25.5% for those on Zepbound [1]. A wider field of approved options would give patients and prescribers more to choose from.
What happens next
Lilly is scheduled to present data from the Phase 3 TRIUMPH-1 trial in obesity and the TRANSCEND-T2D-1 trial in diabetes at the American Diabetes Association's 2026 Scientific Sessions in New Orleans [1]. Novo Nordisk is also presenting at the meeting, including Phase 3 REIMAGINE 1, 2 and 3 data on CagriSema in diabetes [1].
No FDA submission date or approval timeline for retatrutide has been reported [1].
Sources
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