Melanotan II

Overview

Melanotan II is a synthetic, ring-shaped analog of alpha-melanocyte stimulating hormone (alpha-MSH), the body's own signal for producing melanin pigment in the skin. It contains seven amino acids, including substitutions that make it far more potent and longer acting than natural alpha-MSH.

Unlike natural signals that act mainly where they are needed, Melanotan II is non-selective. It activates several melanocortin receptors: MC1R on pigment cells, which drives tanning, and MC3R and MC4R in the brain, which influence appetite, sexual function and other processes. That spread of targets explains both what early studies observed (skin darkening and spontaneous erections) and why side effects such as nausea, stretching and yawning appeared.

Human research is limited to a few very small studies from the 1990s at the University of Arizona. Since then the compound has spread mainly as an unlicensed "tanning injection" sold online. Most recent literature about it consists of case reports of harm, analyses of illicit products and reviews by dermatologists and toxicologists, rather than controlled trials.

Melanotan II has never been approved as a medicine. Two related compounds went on to separate development and approval, which is covered in the history section below.

Research history

In the 1980s, chemist Victor Hruby and biologist Mac Hadley at the University of Arizona set out to design more potent and durable versions of alpha-MSH, partly to explore sunless tanning as a way to reduce skin cancer risk. In 1989 their group described a series of cyclic lactam analogs, among them the compound later named Melanotan II, which was many times more potent than alpha-MSH in lizard skin assays and showed prolonged activity (Al-Obeidi 1989).

A pilot phase 1 study in 1996 gave the compound to three healthy men. It darkened skin in two of them, and investigators also recorded nausea, a stretching and yawning complex, and unexpected spontaneous erections (Dorr 1996). That observation redirected research toward sexual function. A small crossover trial in men with psychogenic erectile dysfunction followed (Wessells 1998).

Development then split. A linear analog, Melanotan I, is now known as afamelanotide. It was approved by the EMA in 2014 and the FDA in 2019 for use in adults with erythropoietic protoporphyria, a rare light-sensitivity disorder. A Melanotan II analog, PT-141, became bremelanotide, approved by the FDA in 2019 for acquired, generalized hypoactive sexual desire disorder in premenopausal women (Hadley 2006 describes this lineage). Melanotan II itself was not taken forward.

In the years since, dermatologists and toxicologists have documented its unregulated use for tanning and a growing number of adverse event reports (Habbema 2017).

What published studies have examined

Laboratory and animal studies

Early work used frog and lizard skin assays to measure pigment responses (Al-Obeidi 1989). Melanotan II later became a common research tool in rodent studies of appetite, energy balance and sexual behavior, because it activates brain melanocortin receptors. Those studies use it to probe biology, not to test it as a treatment.

Controlled human studies

• Dorr 1996. A single-blind, placebo-controlled pilot phase 1 study in three healthy men over two weeks. Two developed measurable skin darkening. Side effects included mild nausea, fatigue and somnolence in one participant at the highest dose tested, a stretching and yawning complex, and spontaneous erections lasting hours.
• Wessells 1998. A double-blind, placebo-controlled crossover study in 10 men with psychogenic erectile dysfunction. Eight of 10 developed erections with Melanotan II, and nausea, stretching, yawning and reduced appetite were more common than with placebo.

Taken together, these studies involved 13 people. No larger controlled trial of Melanotan II has been published.

Case reports and safety literature

Much of what is known about Melanotan II safety comes from people who obtained it outside any study.

• Systemic toxicity. A man who injected an internet-bought product, later confirmed as Melanotan II by mass spectrometry, developed a sympathomimetic reaction with rapid heart rate, rhabdomyolysis and kidney dysfunction requiring intensive care (Nelson 2012).
• Melanoma. A 20-year-old woman who used Melanotan II alongside sunbeds was diagnosed with melanoma months later (Hjuler 2014). A review counted four case reports of melanoma arising from existing moles during or shortly after melanotan use, plus many reports of new or changing moles, while noting that a causal link has not been proven (Habbema 2017).
• Priapism. A man developed low-flow priapism after injecting melanotan; he had not recovered erectile function at four weeks (Dreyer 2019).

Open questions

• Cancer risk. Whether Melanotan II raises melanoma risk, particularly combined with UV exposure, is unknown. Case reports cannot establish cause, but no controlled data exist to rule it out.
• Product identity and purity. Illicit products vary, and users usually cannot confirm what they contain. Our guide to reading a certificate of analysis explains how identity is verified.
• Unmeasured harms. The published controlled experience covers 13 people over short periods. Frequency of serious adverse events in real-world use is unknown, and case reports likely capture only a fraction of events.
• Regulatory position. The FDA's compounding review summarized case reports of melanoma, posterior reversible encephalopathy syndrome, sympathomimetic toxidrome and priapism, and several national health authorities have warned against melanotan products.