Trial Overview

Rhythm Pharmaceuticals Inc. (NASDAQ:RYTM) presented preliminary Phase 2 data for setmelanotide in Prader‑Willi syndrome (PWS) at the Endocrine Society’s Annual Meeting in Chicago. The trial enrolled 18 patients aged 6‑23 years; 17 patients remained on active therapy at the 52‑week mark. The six‑month efficacy analysis used a data cut‑off of May 7, 2026.

Efficacy Results – BMI

Across the 17 patients still on therapy, the mean body‑mass‑index (BMI) reduction was 3.06%. Adult participants (n = 9) achieved a mean BMI reduction of 3.11%, with six adults exceeding a 2.5% reduction and four exceeding a 4% reduction. Pediatric participants (n = 7) showed a mean BMI reduction of 3.00% and a mean BMI‑z‑score reduction of 0.35 from baseline; five of the seven pediatric patients achieved a z‑score reduction greater than 0.2.

Body‑Composition Outcomes

Data from 16 patients revealed a mean lean‑mass gain of 0.74% and a mean fat‑mass loss of 4.19%. Among adults, six of nine patients achieved more than a 5% reduction in fat mass, while five of seven pediatric patients gained at least 2.95% lean mass.

Hyperphagia and Anxiety Measures

Eight of ten patients who entered the trial with moderate to severe hyperphagia recorded a reduction of at least seven points on the Hyperphagia Questionnaire for Clinical Trials. Ten of fifteen patients with a baseline score above 11 on the PWS Anxiousness and Distress Behaviors Questionnaire improved by at least 11 points.

Safety Profile

Safety and tolerability outcomes were consistent with the established profile of setmelanotide observed in earlier studies.

Financial Highlights

Rhythm Pharmaceuticals carries a market capitalisation of $6.06 billion. For the first quarter of 2026, the company reported net revenue of $60.1 million, surpassing the consensus estimate of $55.62 million. Earnings per share reflected a net loss of $0.83. Analyst price targets range from $105 to $159. Citizens reaffirmed a Market Outperform rating with a $155 target, while Stifel raised its target to $133 from $131 and maintained a Buy rating, citing over 150 start‑form submissions from roughly 110 unique prescribers in the first six weeks of the hypothalamic obesity launch.

Analyst Commentary

The early Phase 2 data suggest meaningful reductions in BMI, body‑fat composition, and hyperphagia severity, supporting continued development of setmelanotide for PWS.