The oral one
Bivamelagon: an oral MC4R agonist for hypothalamic obesity
Bivamelagon is an investigational oral MC4R agonist — the pill chasing what setmelanotide does by daily injection. In a placebo-controlled Phase 2 trial in acquired hypothalamic obesity, its top dose cut BMI by 9.3% in 14 weeks, and a pivotal Phase 3 is planned.
The system's satiety signal, cut into a pill — the same MC4R lock, reached without a needle.
Every approved melanocortin peptide so far is injected, because the gut dismantles peptides before they can work. Bivamelagon is one of the first serious attempts to get around that for the appetite receptor. It is an investigationaloral, once-daily MC4R agonist — a non-peptide small molecule — and its ambition is simple to state: do by pill what setmelanotide does by daily needle.[1] Rhythm Pharmaceuticals acquired global rights to the compound (then known only as LB54640) from LG Chem in early 2024, paying about $100 million upfront with up to roughly $205 million in milestones on top.[2]
Same target, different route
Bivamelagon and setmelanotide aim at the identical break in the wiring: a melanocortin-4 receptor that has stopped receiving its "you are full" signal, so hunger runs without a brake. Both are agonists that switch MC4R back on. The difference is entirely in the delivery — setmelanotide is a peptide given as a subcutaneous injection every day, while bivamelagon is a small molecule stable enough to survive the gut and be taken as a tablet.[1] For a condition that is lifelong, swapping a daily injection for a daily pill is not a small thing; it is often the difference between a therapy people start and one they stay on.
The Phase 2 result
Bivamelagon’s lead indication is acquired hypothalamic obesity — the severe, hunger-driven weight gain that follows injury to the hypothalamus, for example after surgery for a brain tumour, where the appetite brake is physically severed. Its placebo-controlled Phase 2 trial (SIGNAL) tested three doses over 14 weeks, and the top two beat placebo decisively on the primary measure, change in BMI:[1][3]
| Arm | Change in BMI at 14 weeks | vs placebo |
|---|---|---|
| Bivamelagon 600 mg | −9.3% | p = 0.0004 |
| Bivamelagon 400 mg | −7.7% | p = 0.0002 |
| Bivamelagon 200 mg | −2.7% | p = 0.018 |
| Placebo | +2.2% | — |
The higher-dose groups also reported meaningfully less hunger, and Rhythm framed the BMI reductions as consistent with what setmelanotide achieves in similar patients — an important bar for an oral drug to clear against the injectable it hopes to replace.[1] The trial was small (roughly two dozen patients across four arms), so these are early, company-reported results rather than a definitive read — the caveat that applies to every Phase 2 topline.
Also aimed at genetic obesity
Acquired hypothalamic obesity is the lead, but not the whole plan. Bivamelagon is also in a Phase 2 trial (ROUTE) for genetic obesity caused by defects in the melanocortin pathway itself — variants in POMC, PCSK1, or the leptin receptor (LEPR).[4]These are the same rare conditions where setmelanotide is already approved, so the two drugs are being lined up across an overlapping franchise: the established injection and the oral challenger, aimed at the same biology from different angles. For the genetics behind those conditions, see the genetics pillar.
What about the tan?
Melanocortin agonists tend to come with a bundled side effect — skin hyperpigmentation — because hitting the appetite receptor often means brushing the pigment receptor MC1R as well. Bivamelagon is not fully clean on this: some hyperpigmentation was reported in its Phase 2, though the numbers were small and one case was even in the placebo group.[1] Tellingly, Rhythm is also developing a separate, next-generation agonist, RM-718, engineered to be MC1R-sparing — a once-weekly MC4R-specific molecule designed precisely to deliver the appetite effect without the tan.[6] That two-track approach is a good tell for where the field is heading: not just oral, but selective enough to peel the wanted effect away from the unwanted one.
Where it is headed
Bivamelagon is one of several drugs converging on the same prize — a pill for MC4R-pathway obesity. Palatin is developing its own oral MC4R agonist, PL-7737, though it sits earlier in development.[7] Bivamelagon is currently in front: on the strength of durable Phase 2 extension data and a positive end-of-Phase-2 meeting with the FDA, Rhythm has said it plans to start a pivotal Phase 3 trial in acquired hypothalamic obesity.[5] Nothing here is approved, and a Phase 3 can still fail — but the trajectory, from an in-licensed molecule to a planned pivotal trial in about two years, is a fair snapshot of how fast the melanocortin field is now moving. Track it on the pipeline page.
Education, not a protocol
This page explains an investigational drug and its trial status. It does not provide dosing or usage instructions and is not medical advice. Bivamelagon is not approved; its safety and efficacy are still being established. See the editorial standards.
Common questions
What is bivamelagon?
Bivamelagon (development code LB54640) is an investigational oral, once-daily MC4R agonist — a small molecule that switches on the melanocortin-4 receptor to restore signalling in the brain’s appetite pathway. Rhythm Pharmaceuticals acquired global rights to it from LG Chem in early 2024.
How is bivamelagon different from setmelanotide?
Both are MC4R agonists that aim to repair the same broken "I am full" signal, but they differ in form. Setmelanotide (Imcivree) is a peptide given as a daily subcutaneous injection; bivamelagon is a non-peptide small molecule taken as a once-daily pill — potentially the oral version of the same idea.
What did the Phase 2 trial show?
In a placebo-controlled Phase 2 trial in acquired hypothalamic obesity, the top 600 mg dose of bivamelagon reduced BMI by 9.3% at 14 weeks while placebo rose 2.2%, with the two higher doses statistically significant. Rhythm described the reductions as consistent with those seen with setmelanotide in similar patients.
Is bivamelagon approved?
No. It is investigational and not approved for any use. After a positive end-of-Phase-2 meeting with the FDA, Rhythm has said it plans to begin a pivotal Phase 3 trial in acquired hypothalamic obesity; a separate Phase 2 in genetic (POMC, PCSK1, LEPR) obesity is also underway.
References
- 1.Rhythm Pharmaceuticals. Oral MC4R agonist bivamelagon achieved statistically significant, clinically meaningful BMI reductions in a placebo-controlled Phase 2 trial in acquired hypothalamic obesity. Press release — SIGNAL Phase 2 topline. 2025. link ↗
- 2.Rhythm Pharmaceuticals & LG Chem Life Sciences. Rhythm to acquire global rights to oral MC4R agonist LB54640 (bivamelagon). Press release — in-licensing agreement (~$100M upfront, up to ~$205M milestones). 2024. link ↗
- 3.ClinicalTrials.gov. A study of LB54640 in patients with acquired hypothalamic obesity (SIGNAL). Trial registry — NCT06046443. 2025. link ↗
- 4.ClinicalTrials.gov. A study to assess efficacy and safety of LB54640 in patients with genetic obesity (ROUTE). Trial registry — NCT06041841 (POMC, PCSK1, LEPR). 2025. link ↗
- 5.Rhythm Pharmaceuticals. Fourth quarter and full year 2025 results. Press release — Phase 3 plan and end-of-Phase-2 FDA meeting. 2026. link ↗
- 6.Rhythm Pharmaceuticals. First patient dosed in Phase 1 trial of RM-718, a weekly MC4R-specific agonist. Press release — MC1R-sparing next-generation agonist. 2024. link ↗
- 7.Palatin Technologies. Oral MC4R agonist PL-7737 receives FDA orphan drug designation for obesity due to leptin receptor deficiency. Press release — competing oral MC4R programme. 2025. link ↗