A triple-action weight-loss drug reports late-stage trial results

Retatrutide, from Eli Lilly, acts on three hormone receptors: GLP-1, GIP, and glucagon. On September 29, The Lancet and the New England Journal of Medicine published its first big late-stage trial results, and they include a split worth noticing.

In the NEJM trial, 2,339 adults with obesity were randomly assigned to one of three doses or a placebo. Average weight change ranged from -17.6% on the lowest dose to -23.7% and -25.0% on the higher ones, compared with -3.9% on placebo.

People who also had type 2 diabetes lost less. In the Lancet's TRIUMPH-2 trial, 1,152 adults with obesity and type 2 diabetes received 4, 9, or 12 mg of retatrutide or a placebo. After 80 weeks, average weight changes were -11.9%, -16.8%, and -18.8%, against -5.1% on placebo. Diarrhea affected 27% to 34% of people taking the drug, versus 13% on placebo.

Two questions remain open. Lilly funded both trials, and both compared retatrutide only with a placebo, so nobody yet knows whether it does better than the drugs people can already get. Retatrutide is also not approved.