Imcivree (setmelanotide)

What it is and how it works

Imcivree (setmelanotide) is a once-daily injection for a small number of specific, diagnosed conditions in which the brain's melanocortin-4 hunger pathway does not work properly. The FDA label covers acquired hypothalamic obesity from age 4, and Bardet-Biedl syndrome or POMC, PCSK1 or leptin-receptor deficiency from age 2. For the POMC, PCSK1 and leptin-receptor indications the label requires genetic testing to confirm the deficiency.

Deep in the brain sits a chain of signals that tells the body when it has eaten enough. Setmelanotide is a melanocortin 4 receptor agonist, which means it switches on the receptor at the end of that chain. In the conditions on the label, the chain is interrupted — a missing hormone, a receptor that cannot hear the signal, or damage to the part of the brain that carries it — and the result is relentless hunger. On the strength of laboratory evidence, the label says the drug may re-establish activity in that pathway to reduce food intake and promote weight loss.

The same drug also acts on a closely related receptor on skin cells, which is why skin darkening is an expected effect rather than a surprise. That is covered further down.

What the trials found

The evidence is not one big trial. It is five separate trials, each in a different group, and the numbers below belong to the specific group they were measured in. Nothing here transfers to obesity in general. Where the published report and the FDA label analysed different numbers of people, both populations are named, because the figures are not interchangeable.

• POMC, PCSK1 or leptin-receptor deficiency — 21 people aged 6 and over, about a year

  Two identically designed trials, both open-label and single-arm: everyone in them took the drug, and there was no control group beyond a four-week blinded withdrawal inside the year. The published primary endpoint was the proportion of participants losing at least 10% of their body weight after about a year: 8 of 10 people (80%) in the POMC and PCSK1 trial reached it, and 5 of 11 (45%) in the leptin-receptor trial. Among the seven participants assessed for hunger in each trial, average scores fell by 27.1% and 43.7%. For the same 10 and 11 people, the FDA label puts the average body-weight change over the year at −23.1% and −9.7%.

• Bardet-Biedl syndrome — 14 weeks blinded, then a year open

  In the published report, which randomised 38 patients aged 6 and over, the primary endpoint was the proportion of those aged 12 and over with Bardet-Biedl syndrome losing at least 10% of body weight at 52 weeks; 32.3% did. The FDA label reports a larger analysis of the same trial — 44 patients with Bardet-Biedl syndrome enrolled, 31 of them analysed across the 52-week treatment period — in which the average change in BMI was −7.9%, with 61.3% reaching a BMI reduction of at least 5% and 38.7% at least 10%. Six patients in the published report had Alström syndrome instead, and the results for them were inconclusive; the label covers Bardet-Biedl syndrome only.

• Acquired hypothalamic obesity — 52 weeks against placebo

  The largest of the trials, and the only one of the three with a placebo group throughout, in people whose obesity followed a hypothalamic tumour, lesion or injury. In the published report, which randomised 120 people aged 4 to 66 two-to-one, BMI fell 16.5% on treatment and rose 3.3% on placebo over 52 weeks, and daily hunger scores fell further on treatment as well. The FDA label reports a larger analysis of the same trial, in 142 randomised patients: 76% of treated patients reached a BMI reduction of at least 5% at 52 weeks and 61% reached at least 10%, against 10% and 5% on placebo.

A separate 52-week trial in 12 children aged 2 to under 6 supported the lower end of the age range. Across all of these, the trials measured BMI or body weight and self-reported hunger. None of them was long enough or large enough to measure whether the drug changes long-term health outcomes.

Side effects, with rates

Side effects are common and the rates are high, partly because these are very small groups where one patient moves the percentage a lot. In the two open-label trials in POMC, PCSK1 and leptin-receptor deficiency — 27 patients in total — the label records:

In the Bardet-Biedl syndrome trial the pattern was similar — skin hyperpigmentation in 63% and injection site reactions in 51% over the 52-week treatment period. In the placebo-controlled trial in acquired hypothalamic obesity, where there is something to compare against, skin hyperpigmentation was reported by 58% on treatment versus 10% on placebo, nausea by 55% versus 25%, and vomiting by 38% versus 19%.

The label carries six warnings. Two of them are the ones people are least likely to expect:

• →Skin darkening and moles. Generalised or focal increases in skin pigmentation occurred in the majority of treated patients. The label says this reverses when the drug is stopped, that new moles may develop or existing ones darken, and it asks prescribers to perform a full-body skin examination before starting and periodically during treatment.
• →Sexual adverse reactions. Spontaneous erections and increased frequency of erections in males, and sexual arousal reactions in females, occurred in the trials. The label tells patients to seek emergency medical attention for an erection lasting longer than four hours.

The other four are depression and suicidal ideation, with monitoring for new or worsening symptoms; serious hypersensitivity reactions including anaphylaxis; acute adrenal insufficiency in patients with acquired hypothalamic obesity and existing adrenal insufficiency, reported in 5% of treated patients and none on placebo; and sodium imbalance in those who also have central diabetes insipidus, where low sodium was reported in 6% of treated patients versus 2% on placebo. A prior serious hypersensitivity reaction to setmelanotide or to any of the excipients in the injection is the label’s only contraindication.

What taking it actually involves

• →A daily injection, not a weekly one. It goes under the skin of the abdomen, thigh or arm, at the beginning of the day, with or without food, rotating to a different site each day. Patients and caregivers are trained on the technique before starting.
• →Dose stepping. Treatment starts low and rises over a few weeks to the label’s maintenance dose of 3 mg a day for everyone aged 6 and over. Children under 6 are dosed by body weight. Severe kidney impairment calls for a lower dose, and the label does not recommend the drug at all in end-stage renal disease, or in acquired hypothalamic obesity with severe kidney impairment.
• →Fridge storage. Unopened vials live in the refrigerator at 2 to 8°C and can sit at room temperature for up to 30 days. Once a vial is punctured it is discarded after 30 days.
• →Skin checks. A full-body skin examination before starting and periodically afterwards is part of the label, not an optional extra.
• →Genetic testing. For the POMC, PCSK1 and leptin-receptor indications the deficiency is confirmed by genetic testing. The label notes there is no FDA-approved test for detecting variants in those genes.

Cost and availability

The drug is made for Rhythm Pharmaceuticals, Inc. and is dispensed as a 10 mg/mL solution in a single-millilitre multiple-dose vial. Because both the diagnosis and the prescription sit with specialist endocrinology and genetics clinics, the practical route to it starts with a referral rather than with a pharmacy.

How it sits in the wider evidence

The percentages on this page look larger than the ones on the GLP-1 pages, and it would be a mistake to read anything into that. These trials enrolled tens of people with a single named condition, mostly without a placebo group, and measured them for a year. The large obesity trials enrolled thousands of people with common obesity against placebo. Different populations, different designs, different questions — the numbers are not comparable in either direction.

What this treatment does show is something the wider field has been circling for years: that some obesity has a single identifiable cause, and that when the cause is known the response to a drug aimed at it can be large. The conditions on this label are rare. The label’s own limitations-of-use section is the boundary, and it is written in plain terms — for other types of obesity, the drug would not be expected to be effective.

If hunger that never switches off has been a feature of your or your child’s life since early childhood, that is a reason to raise genetic and endocrine causes with a doctor — not a reason to expect this particular drug. Whether any of this applies is a clinical judgement, made with a specialist and a test result, not from a web page.

Common questions

Built with agentic AI tools and not a substitute for medical advice

Last reviewed: September 2026