The Food and Drug Administration has widened use of a drug for rare forms of obesity in a decision that could significantly strengthen the sales outlook for its developer, Rhythm Pharmaceuticals.
The FDA on Friday cleared use of Imcivree, a one-daily injection, for adults and children at least 4 years of age with a type of obesity driven by injury to the hypothalamic region of the brain. In clinical testing, Rhythm’s drug helped people with this “acquired hypothalamic obesity” lose about 18 percentage points more of their body weight than placebo recipients. It’s now the first medication available for the condition.
“This is a transformative milestone for Rhythm and reinforces our commitment to bringing meaningful therapies to patients living with rare MC4R pathway diseases,” said Rhythm CEO David Meeker in a statement, referring to the biological pathway Imcivree acts on.
The clearance marks a step forward for a company whose value has more than quintupled since going public nearly a decade ago.
Rhythm already markets Imcivree for multiple rare, genetically driven forms of obesity under approvals handed down in 2020 and 2022. Net revenue has steadily grown since, topping $130 million in 2024 and then about $195 million last year. But Rhythm still posted a net loss of about $202 million in 2025 as well, a deficit the company could reduce with the help of Thursday’s approval.
Wall Street analysts believe acquired hypothalamic obesity represents a market opportunity north of $1 billion. Rhythm executives have previously said they’d already identified around 2,000 diagnosed or suspected U.S. patients with the condition, and expect the total number to be closer to 10,000. Analysts have also pointed to a key differentiating factor between their condition and the kind of general obesity treated with GLP-1 drugs, as it’s driven by ultra-fast weight gain that might now be addressed with a targeted therapy.
Rather than modulate gut hormones as GLP-1 medications do, Rhythm’s shot activates the melatonin-4 receptor, or MC4R, which regulates hunger and is defective in people with certain genetic mutations.
There was some investor trepidation leading up to the decision, however. The FDA in October asked for additional analyses of the efficacy data in Rhythm’s trial, a “major amendment” to the company’s filing that delayed a decision by three months. That request, combined with a “less predictable FDA” of late, may have caused what’s been recent volatility in Rhythm’s share, wrote Stifel analyst Paul Matteis. Negative Phase 3 results reported earlier this week in a different indication also closed off another opportunity to expand Imcivree’s use.
Yet Rhythm received a clearance in acquired hypothalamic obesity with a label that looks “clean on safety,” wrote Leerink Partners’ Thomas Smith. Newly recommended precautions include monitoring for sodium imbalances and a sudden drop in cortisol levels, but those safeguards were “consistent” with what Rhythm executives had expected, Stifel’s Matteis added.
Imcivree’s sales trajectory is now the “key question” going forward, Matteis wrote. Consensus estimates have the drug generating $40 million from the new indication in 2026, but management cautioned investors on a conference call Thursday to expect a “slow and steady launch,” wrote Jefferies’ Dennis Ding.
Rhythm shares climbed roughly 6%, to $96 apiece, in early trading Friday.
