Melanotan I vs Melanotan II: Tanning Peptides Compared

What Are the Melanotans?

Melanotan I and Melanotan II were both developed at the University of Arizona in the late 1980s and early 1990s. The original goal was simple: could you protect fair-skinned people from skin cancer by stimulating their natural tanning response before sun exposure?

Both compounds are synthetic analogues of alpha-melanocyte-stimulating hormone (α-MSH) — a naturally occurring neuropeptide that activates melanocortin receptors in the skin to increase melanin production. But the two compounds diverged significantly in their receptor selectivity and research trajectories.

The Melanocortin Receptor System

To understand the difference between the Melanotans, you need to understand the five melanocortin receptor subtypes:

• MC1R: Located in skin melanocytes — controls skin and hair pigmentation
• MC2R: Located in adrenal glands — regulated by ACTH
• MC3R: Located in the brain and gut — involved in energy balance and feeding
• MC4R: Located in the brain — key regulator of appetite, sexual function, and autonomic activity
• MC5R: Located in exocrine glands — involved in sebum production and immune function

The key distinction: Melanotan I is highly selective for MC1R. Melanotan II activates MC1R, MC3R, MC4R, and MC5R.

Melanotan I (Afamelanotide)

Melanotan I, now known by its INN name afamelanotide, is the more targeted compound. Its high MC1R selectivity means its primary effect is melanin production in skin cells — exactly what the original research program aimed for.

Key research findings for Melanotan I:

• Received European regulatory approval (as Scenesse) for erythropoietic protoporphyria (EPP) — a rare genetic disorder causing extreme sunlight sensitivity
• Clinical trials showed significant reduction in phototoxic reactions in EPP patients
• Also studied for solar urticaria and polymorphous light eruption
• Minimal sexual side effects due to low MC4R activity
• Nausea is the primary reported side effect

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Melanotan II

Melanotan II is a cyclic analogue with broader receptor activity. It produces melanogenesis (tanning) through MC1R activation, but its activity at MC4R produces significant additional effects:

• Sexual arousal: MC4R activation in the hypothalamus stimulates sexual function — spontaneous erections in men, increased sexual desire in both sexes
• Appetite suppression: MC3R/MC4R activation reduces food intake
• Flushing and nausea: More pronounced than Melanotan I due to broader receptor activity
• Darkening of existing moles: A documented effect requiring monitoring

Melanotan II’s MC4R activity led to a spin-off development program that produced PT-141 (bremelanotide) — a compound stripped of the tanning effect and specifically developed for sexual dysfunction. PT-141 received FDA approval for hypoactive sexual desire disorder in women (Vyleesi, 2019).

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Side-by-Side Comparison

Research Applications

Melanotan I is the more clinically validated compound, with an approved use case and extensive human safety data from EPP trials. It’s the appropriate reference compound for photoprotection and pigmentation research.

Melanotan II remains a research compound with a broader mechanistic profile. Its dual tanning/sexual function effects make it a useful tool for studying melanocortin receptor pharmacology — particularly MC4R biology, which has applications in obesity, sexual dysfunction, and autonomic regulation research.

Written by the NorthPeptide Research Team