Setmelanotide (Imcivree): MC4R Agonist for Genetic Obesity
Cyclic peptide agonist of the melanocortin-4 receptor. FDA-approved for specific rare genetic obesity syndromes.
✅ Approved
- Full name
- Setmelanotide (RM-493)
- Class
- MC4R agonist (cyclic octapeptide)
- Half-life
- ~11 hours
- Route
- Subcutaneous daily
- Brand names
- Imcivree (Rhythm Pharmaceuticals)
- Regulatory status
- FDA-approved 2020 (POMC, PCSK1, LEPR deficiency); 2022 (Bardet-Biedl syndrome); 19 March 2026 (acquired hypothalamic obesity, ages 4+, based on Phase 3 TRANSCEND).
What it is
Setmelanotide is a selective agonist of the melanocortin-4 receptor (MC4R), a critical regulator of the hypothalamic energy-balance pathway. It is approved for rare monogenic obesity caused by upstream defects in this pathway where endogenous MC4R stimulation is deficient.
How it works
The leptin→POMC→MSH→MC4R pathway normally signals satiety. Mutations in POMC, PCSK1, LEPR, or associated Bardet-Biedl proteins impair this signalling and cause extreme hyperphagia and early-onset obesity. Setmelanotide bypasses the upstream defect by directly activating MC4R.
Not effective for common (polygenic) obesity — patients must have a confirmed genetic diagnosis. Genetic testing is a prerequisite for prescribing.
What the research shows
Pivotal Phase 3 trials in rare obesity syndromes led to orphan-designation approvals.
Clément K. et al. (2020) — POMC/LEPR deficiency Phase 3
Clément K. et al., Lancet Diabetes Endocrinol 2020;8:960–970. 👥 Human studies
21 patients with biallelic POMC, PCSK1 or LEPR deficiency received setmelanotide for up to 52 weeks.
80% of POMC-deficient patients and 45% of LEPR-deficient patients achieved ≥10% weight loss at 1 year. Hunger scores improved substantially.
Limitations: Tiny population; open-label; very rare indications.
Haqq AM et al. (2022) — Bardet-Biedl syndrome Phase 3
Haqq A.M. et al., Lancet Diabetes Endocrinol 2022;10:859–868. 👥 Human studies
44 patients ≥6 years with Bardet-Biedl syndrome underwent 52 weeks of treatment.
32.3% achieved ≥10% weight loss; mean BMI reduction 7.9%. Hunger scores fell.
Limitations: Injection-site reactions, skin hyperpigmentation common.
Safety and limitations
The most distinctive side effect is hyperpigmentation (MC1R cross-activation), including darkening of skin, new naevi, and lip pigmentation — reversible on discontinuation. Nausea, injection-site reactions, and priapism (rare) also reported.
Cost is exceptionally high (US list > $300,000/year), and treatment is restricted to the approved monogenic indications by payer policies.