POMC → MC1R–MC5R · the melanocortin axis
Five receptors. One ancient signalling system. The most underrated axis in medicine.
It sets your skin's colour, tunes your stress response, gates your hunger, and calms a healing wound — yet most people have never heard its name. The melanocortin axis spent a century as a lab curiosity before becoming one of pharma's hottest frontiers. This is the field guide to the whole system and the drugs now built on it — every claim cited, nothing oversold.
Why now
A biological curiosity just became a drug class.
The melanocortin system was mapped long before anyone could drug it well. That changed fast. The same economy that makes it elegant — one gene, reused across organs — makes it a rare thing in pharmacology: a single family of targets that reaches obesity, pigment disease, inflammation, pain, and sexual function at once.
One generuns the whole systemPOMC is cut, tissue by tissue, into the peptides that set pigment, the stress axis, appetite, and inflammation — read by five receptors, held in check by two natural brakes.
3 in 24 monthsfirst-in-class approvalsFor decades, no drug was designed to hit a melanocortin receptor. Between 2019 and 2020, three did — for a pigment disorder, sexual dysfunction, and genetic obesity.
~12 agentsnow in the clinicThe pipeline is going oral and broad: obesity, dry eye, ulcerative colitis, cancer cachexia — and the first oral MC4R and MC1R drugs are moving through trials.
That is the wager this site is built on: melanocortin pharmacology is early, and early is exactly when a clear, honest map is worth the most. The live pipeline tracks every agent through the clinic, dated and sourced.
Three ways in
Broad overviews that link down into specific, citeable detail — the system, the five receptors, and the drugs built on them.
Start hereThe melanocortin systemHow one precursor — POMC — becomes the peptides that signal across pigmentation, the stress axis, appetite, and inflammation. The whole map in one page.Read →Five switchesMC1R through MC5RA page for each receptor: where it lives, what binds it, what it controls, and what breaks when it fails. The five levers the whole field is built on.Read →The frontierTherapeutics & the pipelineApproved and investigational melanocortin drugs — from setmelanotide and afamelanotide to the oral and anti-inflammatory agents opening the field wide.Read →
The whole map
Every page on the site
56 pages, each one cited: the system, the five receptors, the peptides that ride them, the drugs built on them, and the data that underpins every claim.
The system
- The melanocortin systemHow one precursor, POMC, becomes the peptides that signal across pigment, stress, appetite, and inflammation.
- The POMC cleavage treeAn interactive map of how one precursor is cut into ACTH, the MSH peptides, and β-endorphin — and why the tissue decides which appear.
- Why melanocortinsThe reason this site exists: one ancient gene keeps colour, hunger, stress, and healing in balance.
- Genetics of the melanocortin systemThe variants in MC1R, MC4R and POMC where skin and body-weight genetics turn out to be one pathway.
- Melanocortin control of inflammationThe system’s fourth axis — how MC1R and MC3R calm inflammation, and the drugs built on it.
- Why they make you queasy & tanThe nausea and skin-darkening that come built into the mechanism, not by accident.
- The receptor structuresWhat MC1R–MC5R actually look like — the seven-helix fold, the calcium in the pocket, and how the switch flips on.
The receptors
- The five receptorsMC1R through MC5R — where each one lives, what binds it, and what it controls.
- MC1R — the pigment switchThe receptor behind eumelanin, tanning, and much of skin-cancer risk.
- MC2R — the ACTH receptorThe adrenal odd-one-out that answers only to ACTH and drives cortisol.
- MC3R — energy partitioningThe quieter appetite receptor and its role in how the body divides energy.
- MC4R — the appetite rheostatThe brain’s master switch for hunger and body weight.
- MC5R — exocrine glandsThe least-mapped receptor, governing sebaceous and other exocrine gland function.
The peptides
- α-MSH — the prototype signalThe peptide cut from POMC that activates four of the five receptors, and the template every melanocortin drug copies.
- β-MSH — the human-appetite peptideA broad POMC melanocortin humans make in the brain but lab rodents largely don’t.
- γ-MSH — the MC3R-selective oneThe selective melanocortin whose real job is sodium balance and blood pressure.
- ACTH — the stress-axis melanocortinThe one POMC peptide with its own receptor (MC2R), running the adrenal cortisol axis.
- AgRP — the hunger signalThe peptide that fights α-MSH at MC4R to drive eating — antagonist and inverse agonist in one.
- Agouti protein (ASIP) — the pigment brakeThe natural MC1R blocker that switches skin and coat colour from dark to light.
The drugs
- Therapeutics & the frontierEvery approved melanocortin drug and the pipeline pushing behind them.
- Melanocortin agonistsThe drugs and peptides that switch the system on — endogenous α-MSH, the three approved drugs, and the MC4R-agonist pipeline.
- Setmelanotide (Imcivree)The MC4R drug that repairs a specific break in the appetite circuit.
- Afamelanotide (Scenesse)The first approved EPP drug — an α-MSH copy that builds protective pigment via MC1R.
- Bremelanotide (PT-141)The approved desire drug that began as a tanning peptide’s side effect.
- Melanotan & Melanotan IIThe tanning peptides — the real pharmacology and the documented risks.
- Topical tanningA tan in a cream — the surface stain that fake tan really is, versus the lab agents that switch on real melanin.
- PT-141 vs MelanotanSame molecular family, opposite jobs — the confusion cleared up.
- Dersimelagon (MT-7117)The investigational oral MC1R agonist — the pill chasing afamelanotide’s target.
- Bivamelagon — the oral MC4R agonistThe pill chasing what setmelanotide does by injection; positive Phase 2 in hypothalamic obesity.
- Resomelagon (AP1189)SynAct’s oral biased MC1R/MC3R agonist — built to resolve inflammation without the pigment or cortisol baggage; lead indication rheumatoid arthritis.
- PL-8177 — melanocortin for the gutPalatin’s oral MC1R agonist for ulcerative colitis, acting locally on the colon.
- PL-9643 — a melanocortin eye dropPalatin’s dry-eye candidate; met its co-primary symptom endpoint in Phase 3.
- TCMCB07 — setmelanotide in reverseAn MC4R antagonist for cachexia — the appetite switch run backwards.
- SHU9119 — the classic MC4R antagonistThe research peptide that blocks MC4R to prove melanocortins restrain hunger - the tool behind the appetite discovery.
- PF-07258669 — Pfizer’s oral MC4R antagonistThe structure-designed small-molecule antagonist for appetite loss - reached Phase 1, then Pfizer shelved it for business reasons.
- The melanocortin pipelineA dated snapshot of the drugs moving through development.
Conditions & questions
- Hypothalamic obesityWhen a brain injury physically severs the appetite brake.
- POMC & leptin-receptor deficiencyThe genetic diseases that proved the appetite circuit is real — one missing precursor causing obesity, adrenal failure, and red hair at once.
- Bardet–Biedl syndromeA ciliopathy whose obesity is a melanocortin disease by a back door — the appetite receptor stranded short of the cilium it works on.
- CachexiaThe wasting of serious illness — the appetite rheostat jammed the wrong way, and the reason MC4R antagonists exist.
- Erythropoietic protoporphyria (EPP)The light disease melanocortins learned to treat — where a deficient heme enzyme turns sunlight into pain, and MC1R pharmacology first became medicine.
- VitiligoWhen the pigment cells are destroyed, not just switched off — and why the melanocortin fix is afamelanotide paired with phototherapy.
- Addison’s disease & skin bronzingWhy a cortisol-deficiency disease darkens the skin — ACTH carries α-MSH inside it, so the rescue signal is overheard by MC1R.
- GLP-1 drugs & appetiteWhere Ozempic and Wegovy plug into the melanocortin circuit.
- Melanocortins & sexual functionWhy the appetite receptor also reaches desire — the central MC4R pathway, and the tanning-peptide accident that became a drug.
- Red hair, MC1R & painWhy the pigment gene reaches into pain, anaesthesia, and the dentist’s chair.
- Why oral peptides mostly don’t workRoute, bioavailability, and why every approved melanocortin peptide is injected.
- Why there’s no clean tanning drugPotent melanocortin drugs that build pigment exist — but none that hit MC1R alone. Why a selective MC1R agonist is so hard to make.
- The trouble with MC-receptor antibodiesWhy melanocortin-receptor antibodies so often fail to be specific — and the evidence ladder that tells a trustworthy reagent from a decorative one.
- Dose, delivery & the peakAn interactive model of why timing drives the side effects.
Data & tools
- The binding matrixHow tightly every ligand holds each of the five receptors — the cited numbers behind the words.
- The selectivity visualizerPick any ligand to see its binding fingerprint across MC1R–MC5R and its selectivity window — the fold-gap that decides whether a clean drug is possible.
- Receptor–ligand explorerAn interactive map of what binds which receptor, and how.
- GlossaryPlain-language definitions of every melanocortin term used across the site.
About
Reverent on the science. Sceptical on the page.
Reverence only counts if it survives the citations. Every page carries a visible author and a last-updated date. Therapeutic and pipeline claims are checked against current sources before publication, and where the science is uncertain or contested, the page says so — rather than papering over it. When the frontier is genuinely unsettled, we call it the frontier, not a sure thing.
This is an educational resource, not medical advice. Read the editorial standards →