Setmelanotide

Definition

Setmelanotide is a synthetic melanocortin 4 receptor agonist marketed as Imcivree. It acts on the same receptor pathway as PT-141 and Melanotan II, and unlike either of them it was developed for body weight rather than for sexual function or pigmentation.

The distinction that matters here is not chemical but regulatory. Setmelanotide is an approved obesity drug whose label excludes ordinary obesity, which makes it the clearest case in this index of an approval that is narrower than the condition it appears to treat.

Evidence

The trial record is the development program and it is small by design, because the populations are rare. Across four name variants PubMed returns 243 indexed records, of which 153 carry the Humans subject heading, 19 the clinical-trial publication type and 6 the randomized-controlled-trial type ^[1]. All nineteen were opened and read; seventeen name the molecule and two are matches on the search rather than on the compound, a puberty adipose-depot study and an intranasal oxytocin proteomics paper ^[1].

The registrational evidence is two single-arm phase 3 trials in leptin receptor or proopiomelanocortin deficiency ^[2], and a randomized, double-blind, placebo-controlled phase 3 trial in Bardet-Biedl and Alström syndromes ^[3]. A single-arm design is what a disease affecting a few hundred identified patients permits; it is also a weaker instrument than a controlled one, and the label rests on both kinds.

The indication has widened twice since approval and each widening carries its own trial. A one-year open-label phase 3 extended the population down to children aged two to five years ^[4], and acquired hypothalamic obesity was added on the strength of a phase 2 followed by a randomized trial reported in 2026 ^[5]. The earliest human work in the set is a 2015 study measuring resting energy expenditure in obese adults ^[6], which is the pharmacology rather than the indication.

Side effects

The Imcivree label names the adverse reactions reported in at least 20 percent of treated patients in at least one indication: skin darkening, injection site reactions, nausea, headache, diarrhea, abdominal pain, vomiting, depression and spontaneous penile erection ^[10]. The label carries no boxed warning; the drug is contraindicated only for people who have had a serious hypersensitivity reaction to setmelanotide or to an ingredient of the product ^[10].

Skin darkening is the effect most specific to this drug. Setmelanotide also acts on the melanocortin 1 receptor in pigment cells, and the label reports generalized or focal darkening in the majority of treated patients in clinical trials, reversible after the drug is stopped, along with new moles or darkening of existing ones; it calls for a full-body skin examination before and periodically during treatment ^[10].

The other warnings cover sexual arousal effects, including spontaneous erections, with any erection lasting longer than four hours treated as an emergency; depression and suicidal thoughts, with monitoring for new or worsening mood changes; and serious allergic reactions, including anaphylaxis ^[10]. In acquired hypothalamic obesity the label adds two population-specific risks: serious acute adrenal insufficiency in 5 percent of treated patients with secondary adrenal insufficiency against none on placebo, and sodium imbalance in patients who also have central diabetes insipidus ^[10].

Educational summary of the cited sources, not medical advice; a prescriber weighs these risks against a person’s own history.

Lawful access

The lawful supply route is the approved product. FDA approved setmelanotide injection under new drug application 213793 on November 25, 2020 as a Type 1 new molecular entity, and Drugs@FDA records Imcivree as a subcutaneous solution of setmelanotide acetate at 10 mg base per mL, sponsored by Rhythm and marketed as prescription-only ^[7]. Three efficacy supplements have been approved since, dated June 16, 2022, December 20, 2024 and March 19, 2026 ^[7].

The label states who it is for, and states separately who it is not for. In the version effective April 1, 2026 the product is indicated "to reduce excess body weight and maintain weight reduction long term" in patients aged four years and older with acquired hypothalamic obesity and aged two years and older with obesity due to Bardet-Biedl syndrome or to confirmed proopiomelanocortin, proprotein convertase subtilisin/kexin type 1 or leptin receptor deficiency ^[8]. Its limitations of use say the product "is not indicated for the treatment of patients with the following conditions as IMCIVREE would not be expected to be effective", and name among them "[o]ther types of obesity not related to acquired HO, BBS or POMC, PCSK1 or LEPR deficiency, including obesity associated with other genetic syndromes and general (polygenic) obesity" ^[8].

Compounding does not arise for this molecule. Setmelanotide sits in no category of the section 503A bulks list published May 14, 2026 and on no 503B list ^[9]; an approved product exists, which is the condition under which the bulks question is not asked.

Related molecules

Setmelanotide is filed with the melanocortins beside PT-141 and Melanotan II. The three together make a pattern worth reading as one: both approved members of this class hold labels for narrowly defined populations, and the member with the widest market has no lawful route at all. The approved peptide drugs table places this product beside the rest of the approved set, and the human trial record shows the census behind the count above.

Readers arriving from the weight-loss side should compare it with the GLP-1 receptor agonists, which are approved for general obesity on conditions this label explicitly excludes. The review of peptides for weight loss by US legal status places every molecule marketed for weight in one table.

Elsewhere in this index