Carl read the papersWhat it actually is
Setmelanotide is a cyclic 8-amino-acid peptide modelled on alpha-MSH, a natural melanocortin hormone. It switches on the melanocortin-4 receptor (MC4R), a brain receptor involved in hunger, fullness and energy use.
It is approved as Imcivree for a short list: obesity due to POMC, PCSK1 or LEPR deficiency, Bardet-Biedl syndrome, and since March 2026 in the US (and now also in the EU), acquired hypothalamic obesity (after a tumour, lesion or injury to the hypothalamus). In each, the signal that should switch MC4R on is weak or missing, so the drug supplies it at the receptor.
How it’s thought to work
- MC4R agonism — Activates MC4 receptors in the brain involved in hunger, satiety and energy expenditure.
- Downstream of the fault — In POMC, PCSK1 or LEPR deficiency, the upstream signal to MC4R is missing. Setmelanotide acts on the receptor itself, past the broken link.
- Energy burn — In 12 obese adults, a 72-hour infusion raised resting energy expenditure by 6.4% (about 111 kcal a day) and shifted fuel use towards fat.
- MC1R spill-over — It has about 20-fold less activity at MC1R, the skin-pigment receptor. Less is not none, so skin and moles darken.
What the research says
The trials are small because the diseases are rare, but the effects are big. In the POMC and LEPR phase 3 trials, 8 of 10 POMC patients and 5 of 11 LEPR patients lost at least 10% of body weight at about a year. In Bardet-Biedl syndrome, 32.3% of patients aged 12 and over reached 10% weight loss at 52 weeks. The biggest is TRANSCEND in acquired hypothalamic obesity (NEJM 2026): BMI fell 16.5% on setmelanotide against a 3.3% rise on placebo at 52 weeks. What it lacks is evidence in ordinary obesity, and its label says it would not be expected to work there.
- POMC deficiency (n=10): 80% lost at least 10% of body weight at about 1 year; LEPR deficiency (n=11): 45%.
- Bardet-Biedl syndrome phase 3: 32.3% of patients 12 and over reached at least 10% weight loss at 52 weeks.
- TRANSCEND, hypothalamic obesity (n=120): BMI -16.5% vs +3.3% on placebo; serious adverse events 28% vs 8%.
- Label: not indicated for general (polygenic) obesity, where it 'would not be expected to be effective'.
Reported protocols
These are the doses the peptide community actually reports running (Reddit & forums), alongside published research — logged for education, not as a recommendation to use.
| Parameter | Commonly reported range |
|---|---|
| Label dose, 12+ (BBS or POMC/PCSK1/LEPR) | 2 mg once daily for 2 weeks, then 3 mg once daily; back to 2 mg if 3 mg is not tolerated |
| Label dose, 2 to 11 years (BBS or POMC/PCSK1/LEPR) | Ages 6 to 11: 1 mg once daily for 2 weeks, then 2 mg, then 3 mg maintenance if tolerated. Ages 2 to 5: 0.5 mg once daily to start, with the maintenance dose set by body weight |
| Hypothalamic obesity | Starts lower: 0.5 mg once daily for 2 weeks, then stepped up per the label table to 3 mg daily from age 6 (weight-based for ages 4 to 5) |
| Frequency | Once daily, at the beginning of the day, with or without food |
| Route | Subcutaneous only (abdomen, thigh or arm, new site daily); never into a vein or muscle |
| Community dose | Not established. The one off-label dose we found was a single 500 mcg black-market injection, taken for its erection side effect (one Reddit post). One person, one dose, not a protocol |
| Prescription | A prescription orphan drug that needs a confirmed diagnosis |
Common use cases
| Goal | Community protocol notes |
|---|---|
| POMC, PCSK1 or LEPR deficiency obesity | the original approval; needs genetic confirmation |
| Bardet-Biedl syndrome | approved from age 2 |
| Acquired hypothalamic obesity | approved in the US from March 2026, age 4 and up |
Mixing it (reconstitution)
Freeze-dried peptides must be reconstituted with bacteriostatic water before they can be measured. Carl’s calculator turns “mg in the vial + ml of water + target dose” into “units on the syringe” — and tells you how long the vial lasts.
→ Open the Reconstitution Calculator
Injection & handling
Once a day, first thing, from a 1 mL multi-dose vial holding 10 mg, so 3 mg is 0.3 mL. Subcutaneous into the abdomen, thigh or arm, a different site each day, and never into a vein or muscle. The label wants a full skin check before starting and regularly after, because of darkening skin and new or changing moles. It also flags mood: watch for depression or suicidal thoughts. Spontaneous erections are a listed side effect, and one lasting over 4 hours is an emergency. Unopened vials live in the fridge.
Stacks it appears in
- With PT-141 or Melanotan — Same receptor family and overlapping side effects: PT-141's own label lists nausea and skin hyperpigmentation too. We found no study of them together.
- Switched from a GLP-1 (one case) — A 2026 case report described a man with Bardet-Biedl syndrome who lost 3.4% on liraglutide, then reached 10.5% below baseline after 12 months on setmelanotide. Sequential, one patient, under specialists; not a stack.
Sources
- FDA label: Imcivree (DailyMed, Apr 2026)
- Drugs@FDA: NDA 213793 (Imcivree)
- Rhythm Pharmaceuticals 8-K press release: FDA approval for acquired hypothalamic obesity (19 Mar 2026)
- EMA: Imcivree EPAR
- Clement et al., setmelanotide in POMC/LEPR deficiency, Lancet Diabetes Endocrinol 2020 (PMID 33137293)
- Haqq et al., setmelanotide in BBS and Alstrom, Lancet Diabetes Endocrinol 2022 (PMID 36356613)
- Miller et al., TRANSCEND, setmelanotide in acquired hypothalamic obesity, N Engl J Med 2026 (PMID 42418774)
- Chen et al., RM-493 increases resting energy expenditure, J Clin Endocrinol Metab 2015 (PMID 25675384)
- Pasquariello et al., sequential liraglutide and setmelanotide in BBS, case report, Nephron 2026 (PMID 42743093)
- FDA label: Vyleesi (bremelanotide, PT-141)
- ClinicalTrials.gov NCT05774756 (TRANSCEND)
- SAHPRA: Peptide Products, Public Information (May 2026)
- WADA 2026 Prohibited List
