Melanotan 1 vs Melanotan 2: One Became a Medicine, One Never Did

Melanotan 1 and Melanotan 2 are both synthetic versions of the hormone that darkens skin, but only one of them became a medicine. Melanotan 1 is afamelanotide, sold on prescription as an implant for a rare light-sensitivity disorder. Melanotan 2 has never been approved anywhere.

The shared name suggests two strengths of the same thing. They are different molecules, they act on different sets of receptors, and the evidence behind each has almost nothing in common. This comparison covers what each one is, where the receptor difference comes from, and what the research does and does not show.

What each one is

Both are analogues of alpha-melanocyte-stimulating hormone (alpha-MSH), the natural peptide that signals pigment cells to make melanin. Native alpha-MSH breaks down quickly, which is what both designs were trying to fix.

• Melanotan 1 (afamelanotide, MT-1) is a linear, thirteen-residue analogue of alpha-MSH with two substitutions: norleucine at position 4 and D-phenylalanine at position 7. Those two changes greatly increase its potency and its resistance to degradation compared with the natural hormone. Its approved form is SCENESSE, a controlled-release implant for erythropoietic protoporphyria (EPP). On Peptide Library the name "melanotan-1" resolves to the afamelanotide profile.

• Melanotan 2 (MT-II) is a cyclic lactam analogue of alpha-MSH: smaller, with the chain closed into a ring. It is sold only as a research chemical, is used illicitly for tanning and libido, and is not approved in any jurisdiction. The Melanotan II profile and the Melanotan 2 guide cover it in more depth.

The practical consequence of the name overlap is that people carry Melanotan 1's approval over to Melanotan 2. The site's own dosage review states the point directly: they are different molecules with different pharmacology and different evidence, and treating them as one transfers an approval that Melanotan II does not have.

Receptors: selective versus non-selective

The melanocortin system has five receptors, MC1R to MC5R. Which of them a compound switches on decides what it does, and this is where the two separate.

Afamelanotide is classified as an MC1R agonist. MC1R sits on melanocytes, the pigment-producing cells. Activating it raises cyclic AMP inside the cell and induces a transcription factor (MITF) that drives eumelanin synthesis, the dark brown-black form of melanin. Because this happens downstream of the receptor, it does not need ultraviolet light to start. In EPP the extra eumelanin absorbs and scatters visible light, which is the wavelength range that provokes the painful reactions in that condition.

Melanotan II is a non-selective agonist across MC1R, MC3R, MC4R and MC5R. MC1R accounts for the tanning. MC4R, in the hypothalamus and in spinal pathways, accounts for the appetite suppression and the sexual arousal effects reported with it. That second observation is what led to bremelanotide (PT-141), which was derived from Melanotan II (see the PT-141 guide).

The lack of selectivity is the source of Melanotan II's side-effect profile. It is also a recognised problem in medicinal chemistry: Melanotan II has been used as a starting scaffold in work searching for agonists that are more selective between the human melanocortin receptors (Tomassi 2022).

Side by side

The evidence behind each

Melanotan 1: randomised trials in a rare disease

Afamelanotide's evidence is the conventional kind. Phase 3 randomised trials in EPP, reported in the New England Journal of Medicine, found that the implant increased pain-free exposure to sunlight (Langendonk 2015). Controlled trials of that kind underpin the approval, and the programme has been summarised in several reviews (Minder 2015; Kim 2016).

The approved regimen, per the FDA label, is one 16 mg implant inserted under the skin above the hip bone by a trained professional every two months, in adults with a history of phototoxic reactions from EPP. Afamelanotide has also been trialled alongside narrow-band UVB phototherapy in vitiligo, a phase 2 study with posted results.

In every approved and trialled use, the pigmentation is the mechanism, not the goal: a darker skin is the means of protecting people who are harmed by light.

Melanotan 2: small studies of a different question

Melanotan II has been given to people, but only in small studies from the 1990s, and they were not about tanning. A pilot study in three healthy male volunteers used weight-based subcutaneous doses, starting at 0.01 mg/kg and escalating to a maximum of 0.03 mg/kg, and recorded safety and erectile responses (Dorr 1996). A double-blind, placebo-controlled crossover study then tested it in men with psychogenic erectile dysfunction (Wessells 1998).

Those figures describe what two small studies used. They are not an established dose for anything, and no approved product was ever derived from them.

For pigmentation, which is what Melanotan II is overwhelmingly sold for, there is no completed trial. The only registered pigmentation trial is a phase 2 study of Melanotan II alongside narrow-band UVB in vitiligo, which is recruiting and has no results. Much of what is written about its effects comes from users rather than studies; one dermatology group published a qualitative analysis of online forum discussion of it (Gilhooley 2021), which describes what users report, not what the compound reliably does. The remaining recent work is in rodents, including studies of memory and thermogenesis in mice, and says nothing about people.

Known safety signals

Afamelanotide. The profile records nausea, implant-site reactions, headache and hyperpigmentation. It is prescription-only, and it is approved for EPP rather than for cosmetic use.

Melanotan II. The profile records nausea, flushing, spontaneous erections, new moles and raised blood pressure, along with darkening of existing naevi (moles). Several of these follow directly from its receptor spread: the erections and appetite effects are MC4R effects that a selective MC1R agonist would not be expected to produce. The mole changes attract the most concern, and new or changing moles are worth having checked by a clinician whatever the cause.

A further risk is that Melanotan II is unlicensed and sold without regulatory oversight, so what is in a given vial is not assured. Its sale for human use is prohibited in several jurisdictions, including by the UK MHRA. The grey-market peptides guide covers what that means for product quality.

What the evidence does not show

• That Melanotan 1 and Melanotan 2 are interchangeable. They differ in structure, receptor profile and evidence. An approval for one says nothing about the other.

• That injectable Melanotan 1 is equivalent to the approved implant. The approved product releases 16 mg from an implant over several days. Melanotan 1 sold as a powder for injection is a different dosage form entirely, and the implant's 16 mg does not translate into an injectable dose.

• An approved dose of either for tanning. None exists.

• That Melanotan II's pigmentation effect is safe or effective in trials. It has never been tested for that purpose in a completed study.

• Whether the mole changes seen with Melanotan II translate into a measurable cancer risk. The profile records new moles and darkening of existing ones; the data it holds does not quantify what that means over the long term.

• That the rodent findings apply to people. Mouse studies of memory or thermogenesis are findings about mice.

Frequently asked questions

What is the difference between MT1 and MT2?

MT1 (Melanotan 1, afamelanotide) is a linear alpha-MSH analogue classified as an MC1R agonist, and it is FDA-approved as an implant for erythropoietic protoporphyria. MT2 (Melanotan 2) is a cyclic analogue that activates MC1R, MC3R, MC4R and MC5R, which is why it also affects appetite and sexual function. MT2 has never been approved.

Is Melanotan 1 FDA-approved?

Yes, but only in one form and for one condition: SCENESSE, a 16 mg implant inserted by a trained professional every two months for adults with erythropoietic protoporphyria. It is not approved for tanning, and there is no approved injectable version.

Is Melanotan 2 legal?

It is not approved as a medicine anywhere. The FDA and EMA have warned against its use, the UK MHRA prohibits its sale for human use, and WADA lists it under S0 as a non-approved substance. The guide to peptide legality covers the general picture.

Why does Melanotan 2 cause nausea and erections but Melanotan 1 is described differently?

Because of receptor selectivity. Melanotan II activates MC4R as well as MC1R, and MC4R activity accounts for the appetite and sexual effects. That observation led to bremelanotide. Afamelanotide is classified as acting at MC1R, the pigment receptor, and its recorded side effects are nausea, implant-site reactions, headache and hyperpigmentation.

Has either been studied for tanning?

Not as a cosmetic use. Afamelanotide's trials are in light-sensitivity disorders and vitiligo, where pigmentation protects patients. Melanotan II's published human studies examined erectile function; its only registered pigmentation trial, in vitiligo, has not reported results.