"MT1 or MT2?" is the question tanning forums ask as if it were a choice between two versions of one product. It is a comparison between two different molecules with two different research histories, each of which ended in an approved drug for a disease, not a tan. This page sets the two side by side on the public record. It does not suggest either one: neither is approved for tanning, the vials sold under both names are unregulated, and the safety evidence that exists describes other products. A dermatologist is the right person for any question about a reader's own skin.
The short answer
| Melanotan 1 | Melanotan 2 | |
|---|---|---|
| Structure | Straight chain, 13 amino acids | Ring-shaped (cyclic), 7 residues |
| Molecular weight | ~1,647 | ~1,024 |
| Receptors | Described as a melanocortin-1 receptor (pigment) agonist | Reaches pigment and brain receptors (by its near-twin's label) |
| Tanning research | Several small phase I studies, 1990s–2000s | One pilot, 3 men, 1996 |
| Approved relative | Afamelanotide (Scenesse), same molecule, for erythropoietic protoporphyria | Bremelanotide (Vyleesi), one chemical group different, for low sexual desire |
| Approved for tanning | No | No |
| Registered trials, 27 Sep 2026 | 23 (as afamelanotide) | 1 |
Sources for each row are given in the sections below.
Structure: a chain and a ring
Both are laboratory copies of alpha-melanocyte-stimulating hormone (alpha-MSH), the 13-amino-acid hormone that tells pigment cells to make dark eumelanin, designed at the University of Arizona. They took the copy in two directions.
- Melanotan 1 keeps alpha-MSH's full 13-residue length and changes two building blocks. The FDA label for its approved form gives the sequence Ac-Ser-Tyr-Ser-Nle-Glu-His-(D)Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2, molecular weight 1,646.85.
- Melanotan 2 keeps only the core of the hormone and closes it into a ring. PubChem (CID 92432) gives Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, formula C50H69N15O9, molecular weight 1,024.2.
Peptide Lexicon's entries on melanotan I and melanotan II cover each molecule in more depth.
Receptors: why melanotan 2 does more than tan
There are five melanocortin receptors. MC1R sits on pigment cells; MC4R and MC3R sit mainly in the brain, where they are involved in appetite and sexual function. Where each one sits, and what an obesity drug aimed at MC4R does to skin colour, is explained in how alpha-MSH signals pigment cells.
No regulator-reviewed document describes melanotan 2's receptor profile, because it has never been through approval. Its near-identical relative has. Bremelanotide, sold in the US as Vyleesi, has the structure Ac-Nle-cyclo-(Asp-His-D-Phe-Arg-Trp-Lys-OH), according to its FDA label. Set against PubChem's entry for melanotan 2, the only difference is the last group: -OH (a free acid) on bremelanotide, -NH2 (an amide) on melanotan 2. PubChem's formulas differ by exactly that swap (C50H68N14O10 against C50H69N15O9).
Vyleesi's label states that bremelanotide "nonselectively activates several receptor subtypes with the following order of potency: MC1R, MC4R, MC3R, MC5R, MC2R", and that at its dose "binding to MC1R and MC4R is most relevant". It adds that MC1R binding "leads to melanin expression and increased pigmentation". That is the plainest available account of why melanotan 2's first tanning pilot also recorded spontaneous erections, and why its later trials were about sexual function.
Scenesse's label describes afamelanotide simply as "a melanocortin 1 receptor (MC1-R) agonist". Neither label gives the two drugs' binding strengths side by side, so this page does not rank them.
The research each one had
Melanotan 1 had the longer tanning programme: small phase I studies in the 1990s and 2000s measured tanning, sunburn cells and drug levels, each in a small group of volunteers. It then became afamelanotide and was developed for erythropoietic protoporphyria, a rare disorder in which light causes severe pain. ClinicalTrials.gov listed 23 afamelanotide studies on 27 September 2026, across porphyrias, vitiligo, other light-sensitivity disorders and two healthy-volunteer studies; none studies cosmetic tanning. The detail is on our afamelanotide and Scenesse page.
Melanotan 2 had one tanning study: a pilot in three men (Dorr et al., 1996, PMID 8637402), summarised on our tanning peptides page. Its later trials studied erectile dysfunction, and that line of work produced bremelanotide. ClinicalTrials.gov listed one study of melanotan 2 by name on the same date: a 60-person, placebo-controlled phase 2 trial of melanotan 2 added to narrowband UV-B light therapy in vitiligo, sponsored by Hudson Biotech in China, which began recruiting in February 2026 (NCT07437560). That is a repigmentation study in a skin disease, not a tanning study.
The approved relatives, and what their labels say about skin
The most useful comparison available is between the two labels, because they are the only regulator-reviewed safety tables for anything in this family. They are not labels for melanotan 1 or 2 vials, and they describe supervised use in patients.
| Scenesse (afamelanotide) | Vyleesi (bremelanotide) | |
|---|---|---|
| FDA approval | 8 Oct 2019, NDA 210797 | 21 Jun 2019, NDA 210557 |
| Approved for | Pain-free light exposure in adults with EPP | Acquired, generalised low sexual desire in premenopausal women |
| Given as | 16 mg implant every 2 months, inserted by a trained professional | 1.75 mg self-injection by autoinjector, as needed |
| Nausea | 19% (vs 14% placebo) | 40% of patients using up to 8 doses a month; 13% needed anti-nausea medicine |
| Skin darkening | Hyperpigmentation 4% (vs 0%); moles 4% (vs 2%) | Focal hyperpigmentation 1%, including face, gums and breasts; "resolution was not confirmed in some patients"; higher risk with darker skin and daily dosing |
| Other label warnings | Serious allergic reactions reported; twice-yearly full-body skin examination recommended | Transient blood-pressure rise and heart-rate fall after each dose; not recommended at high cardiovascular risk |
Two readings follow from the table, and both stop short of a verdict. First, pigment change is a labelled effect of both approved relatives, which is expected: both act on MC1R. Second, the drug closest to melanotan 2 carries warnings that have nothing to do with skin, which is consistent with its reach into brain receptors. What neither label can say is what an unregulated vial of either peptide contains or does.
Regulation
| Regulator | Melanotan 1 | Melanotan 2 |
|---|---|---|
| FDA (US) | Approved only as Scenesse, for EPP | Unapproved; warning letter to a seller, 30 Aug 2007 |
| EU | Scenesse authorised 22 Dec 2014, for EPP, under exceptional circumstances | Not authorised |
| MHRA (UK) | — | Injectable melanotan treated as an unauthorised medicine (FOI 24/274, 17 Apr 2024) |
The regulatory record is set out with quotations on our tanning peptides page.
Why "which is safer" has no answer here
Forum threads often treat melanotan 1 as the gentler option because it acts more narrowly. The record does not support turning that into a safety ranking:
- The melanotan 1 safety data are from a manufactured implant given to adults with a disease; the melanotan 2 data are case reports and one three-man pilot. Comparing a trial table with case reports compares evidence types, not drugs.
- The vials sold under both names are, in the UK regulator's words about unauthorised products, of unknown contents. A label on a vial is not a statement of what is in it.
- No study has put the two side by side in healthy people, for tanning or for anything else.
What has been reported in people using unregulated melanotan, counted by source type, is on our melanotan side effects page. Anyone noticing a new or changing mole is best served by a doctor examining it, whatever the cause.