Rhythm Pharmaceuticals announced on June 15 that its weight loss injection Imcivree led to a reduction in body mass index during a Phase 2 study involving patients with Prader-Willi syndrome. The company said these results follow a recent late-stage setback for the drug.
Imcivree, which is already approved for several obesity-related conditions, is Rhythm’s only marketed product and generated $194.8 million in revenue in 2025. In addition to Prader-Willi syndrome, Rhythm is developing Imcivree for other rare and genetic forms of obesity.
At the six-month mark of the Phase 2 trial, patients treated with Imcivree experienced an average decrease of 3.06% in body mass index. Adults saw a mean reduction of 3.11%, while children recorded a drop of 3%. The data were shared Saturday and are scheduled for presentation at the annual meeting of the Endocrine Society.
Body composition analysis indicated that fat mass declined by an average of 4.19% among sixteen participants receiving Imcivree, while lean mass increased by 0.74%. Among pediatric patients, five out of seven showed at least a 2.95% increase in lean mass.
Analysts at Stifel told investors that these outcomes "look better than expected," describing the data as "encouraging." They also said, "The mean BMI reductions was roughly ~1.8% at the time... The data have improved and reflect positive signal for setmelanotide." Stifel further commented on improvements related to hyperphagia—a condition characterized by extreme hunger—measured using the Hyperphagia Questionnaire for Clinical Trials score: "The hyperphagia signal here looks encouraging," although they noted this measure is more subjective than BMI.
Imcivree acts as an MC4 receptor agonist that regulates hunger and energy expenditure while promoting satiety sensations. It was first approved in November 2020 to manage chronic weight issues associated with deficiencies in POMC, PCSK1 or LEPR proteins, and later received approval for use in Bardet-Biedl Syndrome—a rare genetic disorder causing childhood obesity—in 2022.
