Compound family

Melanocortin agonists

In one sentenceFour analogues of the same pigment hormone. Three became approved medicines — for low sexual desire, a rare light-sensitivity disease, and genetic obesity; one stayed a grey-market tanning injection with documented harms.
Compounds4
Best gradeA PT-141
Approved medicines3 of 4
Prohibited in sport0 of 4

What this family is

All four mimic α-melanocyte-stimulating hormone at the melanocortin receptors — MC1 for pigment in skin, MC4 for appetite and sexual arousal in the brain. The 1980s Arizona programme that set out to make a sunless tan produced two: Melanotan I, linear and selective for pigment, and Melanotan II, cyclic and non-selective, which darkened skin and unexpectedly triggered erections. PT-141, bremelanotide, is Melanotan II's metabolite, kept for the sexual effect. Setmelanotide came later and separately, built to hit MC4 alone.

Three of the four are approved medicines. Melanotan I became afamelanotide, an implant for erythropoietic protoporphyria that roughly doubled patients' pain-free time in sunlight in two randomised trials. PT-141 completed two phase 3 trials in 1,267 women and was approved in 2019 for hypoactive sexual desire disorder: small but significant gains in desire, with nausea in 40%. Setmelanotide restores the appetite signal in people with specific genetic defects — 80% of POMC-deficient patients lost a tenth of their weight — on trials of ten and eleven people. Melanotan II never completed later-stage trials. Its harms are documented in the case literature — nausea, uncontrolled erections, darkening and change of moles, and serious events including kidney infarction — which is why regulators warn against it.

None is approved for tanning anywhere, including the one that started as a tanning peptide. PT-141's use in men, and setmelanotide's use in common obesity, are both unapproved and unsupported.

Grade counts across the family: 2 × A · 1 × B · 1 × C · 0 × D. The best grade here, A, means established in humans. How LYO grades →

The compounds, graded

Every member with its best-supported outcome grade, human-trial count and regulatory status. Each opens the full evidence page.

PT-141

A

An approved medicine — for one indication, in one population, with a 40% nausea rate.

Human trials2 phase 3 RCTs (n=1,267)
StatusApproved (Rx, US)

Afamelanotide (Melanotan I)

A

The original tanning peptide — which became an approved medicine for a rare light-sensitivity disease, as a 60-day implant.

Human trials2 phase 3 RCTs (n=168) + long-term registry data
StatusApproved (Rx) — erythropoietic protoporphyria

Setmelanotide

B

An approved obesity peptide — for a few thousand people worldwide with specific genetic defects, on trials of ten and eleven patients.

Human trialsSingle-arm phase 3 trials (n=10, n=11) with placebo-withdrawal; BBS trial (n=38); acquired hypothalamic obesity phase 3 RCT (n=120)
StatusApproved (Rx) — rare genetic obesity; hypothalamic obesity in Canada

Melanotan II

C

A tanning-and-erection peptide with real small-trial signals and real, documented harms.

Human trialsSmall early-phase trials
StatusNot approved

Comparisons

Questions

Is PT-141 the same as Melanotan II?
Closely related — PT-141 is a metabolite of Melanotan II, selected because it keeps the effect on desire without the tanning. One is an approved medicine with two phase 3 trials; the other has never completed late-stage development.
Is Melanotan II legal?
It is not an approved medicine anywhere. Selling it for human use is an offence in the EU and UK, and medicines regulators in several countries have issued specific warnings about it.
What is the difference between Melanotan I and Melanotan II?
Melanotan I is linear and acts mainly on the pigment receptor; it became afamelanotide, an approved implant for a rare light-sensitivity disease. Melanotan II is cyclic and hits several receptors, which gives it the erections and nausea — and it never became a medicine.
Does PT-141 work in men?
The approval and the phase 3 evidence are in premenopausal women. Studies in men, including for erectile function, are small and early; that use is unapproved.

Written and maintained by LYO Research — how pages are written and checked. Reviewed 23 September 2026. Grades count human evidence only. Not medical advice. Correct this page →