Melanotan I vs Melanotan II: Comparing the Tanning Peptides

Melanotan I and Melanotan II share a name, a chemical ancestor, and almost nothing else in terms of regulatory status. Both are synthetic peptides built from alpha-melanocyte-stimulating hormone (alpha-MSH) to darken skin, but one of them went through years of clinical trials and became an approved drug for a specific rare disease. The other is sold on the internet as an injectable “tanning peptide” and has never been approved for any use, anywhere.

Algae bloom, algae farm, cool backgrounds — illustrating Melanotan I vs Melanotan II: Comparing the Tanning Peptides

A shared origin, two very different receptors

Alpha-MSH works by activating melanocortin receptors, a family that includes MC1R (found mainly on melanocytes, the pigment-producing cells in skin) and MC3R/MC4R/MC5R (found in the brain and elsewhere, involved in appetite, energy use, and sexual response). Melanotan I, known in its developed form as afamelanotide, was engineered to be a relatively selective MC1R agonist — it mainly tells melanocytes to produce more melanin, with less spillover into the other receptors. Melanotan II is a shorter, less selective analog that activates MC1R along with MC3R and MC4R, which is exactly why it produces effects afamelanotide mostly doesn’t: appetite suppression, flushing, and spontaneous sexual arousal.

Melanotan I: the one that actually became a drug

Afamelanotide is marketed as Scenesse and is FDA-approved for erythropoietic protoporphyria (EPP), a rare inherited disorder in which even brief sun or light exposure triggers severe burning pain in the skin. It’s delivered as a subcutaneous implant placed by a physician, releasing the peptide gradually over roughly two months, and it’s used to raise the light tolerance of EPP patients — not to produce a cosmetic tan for people who otherwise have normal skin. It took the manufacturer, Clinuvel, well over a decade of trials to get there, and the approved use remains narrow.

The FDA-approved version of this peptide family exists to reduce phototoxic pain in a rare genetic disease, not to produce a cosmetic tan — and it isn’t prescribed for that purpose.

Sample, lab, laboratory — illustrating Melanotan I vs Melanotan II: Comparing the Tanning Peptides

Melanotan II: the one people actually mean by “the tanning peptide”

When people online talk about injecting a peptide to get a tan, they almost always mean Melanotan II, not the approved drug above. It has never completed the approval process anywhere and is sold through gray-market research-chemical vendors with no quality control, no verified purity, and no standardized dosing. Its non-selective receptor activity produces a fairly consistent early-use pattern of nausea and vomiting, facial flushing, and appetite changes, and its MC4R activity is strong enough that spontaneous erections and priapism are a recognized effect — in fact, a related, more MC4R-selective peptide from the same research lineage, bremelanotide, is FDA-approved as Vyleesi for low sexual desire in women, which underscores how real that receptor effect is.

The mole question

The more serious concern with Melanotan II is what melanocyte stimulation can do to existing pigmented lesions. Case reports, including one published in the BMJ, described new or changing moles appearing in people using unlicensed melanotan injections, with some lesions showing atypical features on dermatologic exam. That doesn’t prove Melanotan II causes melanoma, and the case-report literature is too small and too confounded by sun exposure and monitoring bias to draw a firm causal line. But the underlying biology — a drug that pushes melanocytes to produce more pigment — is a plausible mechanism for concern, and it’s the reason dermatologists who see these cases recommend baseline and follow-up skin checks for anyone using it. Buying an unregulated peptide online and injecting it without medical supervision removes exactly the monitoring that would catch a change early.

Test tube, covid-19, mask — illustrating Melanotan I vs Melanotan II: Comparing the Tanning Peptides

Side by side

	Melanotan I (afamelanotide)	Melanotan II
Regulatory status	FDA-approved (as Scenesse)	Not approved anywhere
Receptor selectivity	Relatively selective for MC1R	Non-selective (MC1R, MC3R, MC4R, MC5R)
Approved/studied use	Erythropoietic protoporphyria (EPP)	None; sold illicitly for tanning and libido
Administration	Physician-placed subcutaneous implant	Self-injected, unregulated dosing
Common reported effects	Generally better tolerated at approved doses	Nausea, flushing, appetite loss, spontaneous erections
Key safety signal	Narrow, monitored clinical use	Case reports of changing/darkening moles; product-quality risk

The takeaway

Melanotan I’s clinical history shows the melanocortin pathway can be turned into a legitimate, tightly controlled drug for a specific medical problem. Melanotan II shows what happens when a related molecule skips that entire process and goes straight to unsupervised injection for cosmetic effect: gastrointestinal side effects that are almost universal early on, a real (if unproven) mole-safety signal, and zero assurance about what’s actually in the vial. Anyone using a melanocortin peptide for any reason — approved or not — should be getting their skin checked by a clinician, and anyone considering Melanotan II specifically should weigh that a documented, regulated alternative pathway for pigmentation problems already exists and this isn’t it.