Setmelanotide (Imcivree)
Setmelanotide (Imcivree) is a highly selective MC4R agonist cyclic octapeptide FDA-approved in 2020 for the treatment of obesity caused by POMC, PCSK1, or LEPR deficiency. It restores melanocortin signaling downstream of genetic defects in the leptin-melanocortin pathway.
Setmelanotide, marketed as Imcivree, is a synthetic cyclic octapeptide and highly selective melanocortin 4 receptor (MC4R) agonist. In November 2020, it became the first FDA-approved therapy for chronic weight management in patients with obesity due to proopiomelanocortin (POMC), proprotein convertase subtilisin/kexin type 1 (PCSK1), or leptin receptor (LEPR) deficiency confirmed by genetic testing.
Overview
Setmelanotide was developed from structure-activity relationship studies on the His-D-Phe-Arg-Trp melanocortin pharmacophore, with flanking residues and macrocyclic constraints optimized to achieve high MC4R selectivity (>20-fold over MC3R and >1000-fold over MC1R). This selectivity profile is critical: it maximizes the appetite-suppressing and energy expenditure-enhancing effects of MC4R activation while minimizing the pigmentation (MC1R) and non-target effects associated with non-selective melanocortin agonists like Melanotan II.
The leptin-melanocortin pathway is the primary central regulator of energy homeostasis. Leptin released by adipocytes signals through the leptin receptor (LEPR) on hypothalamic neurons, activating POMC neuron transcription (requiring PCSK1 for POMC processing) to produce alpha-MSH, which activates MC4R to suppress appetite and increase energy expenditure. Genetic deficiency at any step — LEPR, POMC, or PCSK1 — eliminates alpha-MSH/MC4R signaling, causing severe hyperphagia and early-onset obesity. Setmelanotide bypasses these upstream defects by directly activating MC4R, the final receptor in the cascade.
Rhythm Pharmaceuticals received Breakthrough Therapy designation from the FDA, reflecting the absence of any prior therapy for these devastating monogenic obesity disorders.
Mechanism of Action
Setmelanotide acts as a potent and highly selective MC4R agonist:
- MC4R activation: Binding to MC4R in the paraventricular nucleus (PVN) of the hypothalamus activates Gs-coupled adenylyl cyclase, increasing cAMP and activating PKA. This triggers anorexigenic signaling through reduced expression of orexigenic neuropeptides (MCH, orexin) and increased sympathetic outflow to brown adipose tissue, enhancing thermogenesis (Kühnen et al., 2016)
- Dual signaling: MC4R activation by setmelanotide engages both Gs/cAMP/PKA and Gq/PLC/Ca2+ pathways. Both are required for full appetite suppression, as demonstrated by studies showing that biased agonists activating only one pathway produce partial efficacy
- Selectivity advantage: The >1000-fold selectivity for MC4R over MC1R means setmelanotide produces minimal pigmentation at therapeutic doses, unlike non-selective agonists. The >20-fold selectivity over MC3R reduces energy partitioning side effects
- Bypass mechanism: In POMC deficiency, there is no endogenous alpha-MSH to activate MC4R. In LEPR deficiency, leptin cannot stimulate POMC neurons. In PCSK1 deficiency, POMC cannot be processed to alpha-MSH. Setmelanotide directly activates MC4R regardless of these upstream defects, restoring the final effector step
Reconstitution Calculator
Reconstitution Calculator
Calculate your peptide dosing
Set up a clean workspace with all supplies ready.
7x / week for weeks
Research
Alström Syndrome and Other Genetic Obesities
Rhythm Pharmaceuticals has expanded clinical trials to other rare genetic obesity disorders where the melanocortin pathway is disrupted, including Alström syndrome, SH2B1 deficiency, and MC4R partial loss-of-function heterozygous mutations. Phase II/III data are expected through 2026. The MC4R-targeted mechanism may benefit any obesity disorder where reduced melanocortin tone is the proximate cause of hyperphagia.
Not Effective for Common Obesity
Setmelanotide has not demonstrated efficacy for common (polygenic) obesity, where MC4R signaling is intact but overwhelmed by the combined effects of multiple genetic, environmental, and behavioral factors. The drug specifically addresses the pathophysiology of monogenic disorders where MC4R tone is constitutively absent or severely reduced.
POMC Deficiency Obesity
Kühnen et al. (2016) reported the first clinical use of setmelanotide in two patients with POMC deficiency. Both patients had severe early-onset obesity (BMI >50 kg/m2), extreme hyperphagia, and red hair (reflecting absent MC1R stimulation). Treatment with subcutaneous setmelanotide produced dramatic reductions in hunger within the first week. One patient lost 51.0 kg (BMI reduction from 54.7 to 37.3 kg/m2) over 42 weeks; the second lost 20.5 kg over 12 weeks. Both reported transformative improvements in hunger control and quality of life.
Phase III Pivotal Trials
Clément et al. (2020) reported results from two Phase III open-label trials. Study 1 enrolled 10 patients with POMC or PCSK1 deficiency obesity; Study 2 enrolled 11 patients with LEPR deficiency obesity. The primary endpoint was the proportion of patients achieving at least 10% weight loss after approximately 1 year of treatment. In Study 1, 80% of patients achieved the primary endpoint, with mean weight loss of 25.6%. In Study 2, 45.5% of patients with LEPR deficiency achieved at least 10% weight loss, with mean weight loss of 12.5%. Hunger scores (measured by daily hunger questionnaire) were significantly reduced in both studies.
LEPR Deficiency Obesity
Clément et al. (2020) specifically analyzed outcomes in LEPR-deficient patients. These patients have intact POMC neurons but cannot respond to leptin, resulting in constitutively low MC4R tone. Setmelanotide restored MC4R signaling, producing weight loss comparable to bariatric surgery in some patients. The response rate was somewhat lower than in POMC deficiency, likely reflecting the greater complexity of LEPR-mediated signaling beyond the melanocortin pathway.
Bardet-Biedl Syndrome
Haqq et al. (2022) reported Phase III results for setmelanotide in Bardet-Biedl syndrome (BBS), a ciliopathy causing obesity through impaired melanocortin signaling. In 32 BBS patients treated for 52 weeks, 32.3% achieved at least 10% weight loss. The FDA expanded the Imcivree indication to include BBS in June 2022, broadening the eligible patient population.
Safety Profile
The safety profile of setmelanotide has been characterized in Phase III clinical trials across multiple genetic obesity populations:
- Injection site reactions: The most common adverse effect, reported in ~45% of patients. Generally mild (erythema, pruritus, induration) and self-resolving
- Skin hyperpigmentation: Reported in ~35% of patients, reflecting residual MC1R agonist activity despite high MC4R selectivity. Diffuse darkening, particularly in facial skin and existing nevi. Generally mild and does not require treatment discontinuation
- Nausea: Reported in ~15% of patients, significantly lower than with non-selective melanocortin agonists (MT-II: ~50%, bremelanotide: ~40%), reflecting improved MC4R selectivity
- Diarrhea: Reported in ~15% of patients
- Spontaneous penile erection: Reported in male patients, reflecting MC4R-mediated sexual function effects. Generally mild and transient
- Depression and suicidal ideation: Included as a warning in the FDA label based on reported events during clinical trials. Patients require monitoring for mood changes, particularly during dose titration
- Sexual adverse reactions: Spontaneous erections and sexual adverse events require counseling, particularly in pediatric patients (Imcivree is approved for patients aged 6 years and older)
- Contraindications: Should not be used in patients with suspected MC4R-related obesity (these patients have intact but reduced MC4R signaling; further agonism may not be beneficial)
- REMS program: Imcivree is available only through a restricted Risk Evaluation and Mitigation Strategy (REMS) program due to risks of depression, suicidal ideation, and sexual adverse reactions
Pharmacokinetic Profile
Setmelanotide (Imcivree) — Pharmacokinetic Curve
Subcutaneous injection (daily, self-administered)Quick Start
- Route
- Subcutaneous injection (daily, self-administered)
Molecular Structure
- Weight
- 1117.3 Da
- CAS
- 920014-72-8
Research Indications
Metabolic
FDA-approved for obesity due to POMC, PCSK1, or LEPR deficiency. Phase 3 trials showed mean weight loss of 25.6% in POMC deficiency patients over 1 year through MC4R agonism restoring satiety signaling.
Patients with biallelic LEPR deficiency achieved mean weight loss of 12.5% over 1 year. Setmelanotide bypasses defective leptin signaling by directly activating downstream MC4R pathway.
Demonstrated clinically meaningful weight reduction in patients with PCSK1 deficiency, though response is more variable than in POMC deficiency due to broader hormonal dysregulation.
FDA-approved expansion for BBS-associated obesity. Phase 3 trial showed significant BMI reduction in BBS patients, the first pharmacotherapy specifically indicated for this syndromic obesity.
Neurological
Setmelanotide dramatically reduces hunger scores in MC4R pathway deficiency patients. Patients report transformation from constant insatiable hunger to normal appetite patterns within weeks of treatment initiation.
Research Protocols
subcutaneous Injection
Treatment with subcutaneous setmelanotide produced dramatic reductions in hunger within the first week.
Interactions
Peptide Interactions
Setmelanotide acts downstream of leptin signaling in the melanocortin pathway (POMC → α-MSH → MC4R). In patients with leptin receptor deficiency, setmelanotide bypasses the defective leptin signaling to directly activate MC4R, restoring satiety signaling. Source: FDA Imcivree label; StatPearls Setmelanotide.
What to Expect
What to Expect
Effects begin within hours of administration based on half-life of ~11 hours
In 32 BBS patients treated for 52 weeks, 32.3% achieved at least 10% weight loss.
Due to short half-life (~11 hours), effects are expected per-dose; consistent daily administration maintains therapeutic levels
Regular administration schedule required; effects are dose-dependent and do not persist between doses
Quality Indicators
What to look for
- Phase 3 clinical trial data available
- Human clinical trials conducted
- Multiple peer-reviewed studies available
Caution
- Injection site reactions reported
Frequently Asked Questions
References (7)
- [1]Kühnen P, Clément K, Wiegand S, et al Proopiomelanocortin deficiency treated with a melanocortin-4 receptor agonist N Engl J Med (2016)
- [2]Clément K, Biebermann H, Farooqi IS, et al MC4R agonism promotes durable weight loss in patients with leptin receptor deficiency Nat Med (2018)
- [4]Haqq AM, Chung WK, Dolber T, et al Efficacy and safety of setmelanotide in patients with Bardet-Biedl syndrome Diabetes Obes Metab (2022)
- [5]Collet TH, Dubern B, Mokrosinski J, et al Evaluation of a melanocortin-4 receptor agonist (setmelanotide) in MC4R deficiency Mol Metab (2017)
- [6]Clément K, Mosbah H, Poitou C Rare genetic forms of obesity: from gene to therapy Physiol Behav (2020)
- [3]Clément K, van den Akker E, Argente J, et al Efficacy and safety of setmelanotide in individuals with severe obesity due to LEPR or POMC deficiency Lancet Diabetes Endocrinol (2020)
- [7]Clément K, van den Akker E, Argente J, et al — Efficacy and safety of setmelanotide, an MC4R agonist, in individuals with severe obesity due to LEPR or POMC deficiency Lancet Diabetes Endocrinol (2020)
Sermorelin
Sermorelin is a synthetic 29-amino acid analogue of growth hormone-releasing hormone (GHRH) used to assess and stimulate natural growth hormone secretion. It is researched for cardiac repair, bone density, sleep regulation, epilepsy, and age-related GH decline.
SHLP1 (Small Humanin-Like Peptide 1)
SHLP1 is a mitochondria-derived micro-peptide encoded by the 16S rRNA region of the mitochondrial genome with anti-apoptotic and cytoprotective properties, showing research promise in neurodegeneration, metabolic regulation, and aging.