History

Melanotan II was developed in the 1980s at the University of Arizona by a group including chemist Victor Hruby and endocrinologist Mac Hadley, who were engineering stable, potent α-MSH analogues. The original goal was a "sunless tanning" agent to stimulate protective skin pigment and reduce UV exposure; researchers also observed sexual-arousal effects. The university licensed the work to Palatin Technologies, which pursued sexual-dysfunction indications but dropped MT-II around 2000 in favor of the related drug bremelanotide. MT-II itself was never approved as a medicine.

Melanotan II is a synthetic peptide sold online to darken skin (“the tan jab”), suppress appetite, and boost libido. It is not approved as a drug anywhere, and the way people actually use it has never been tested in a controlled trial.

What it is

Melanotan II is a lab-made, cyclic analogue of alpha-melanocyte-stimulating hormone (alpha-MSH). It activates several melanocortin receptors fairly indiscriminately (MC1R through MC5R). MC1R activation drives melanin production in the skin (tanning); MC4R activation in the brain affects appetite and sexual arousal. That receptor promiscuity explains both its range of effects and its messy side-effect profile. It is typically self-injected under the skin; some sell it as a nasal spray. It is distinct from Melanotan I (afamelanotide, brand name Scenesse, an FDA-approved drug for a rare light-sensitivity disorder) and from bremelanotide.

The claims

Marketers and users claim it produces a deep tan with little sun, protects against sunburn, curbs appetite for weight loss, and increases erections and sexual desire.

What the evidence actually shows

The human data are old, small, and narrow. In the 1990s and 2000s, a University of Arizona group ran small placebo-controlled crossover trials in men with erectile dysfunction. In one, 8 of 10 men developed erections after subcutaneous Melanotan II versus placebo; later studies in roughly 20 men reported increased erections and self-reported sexual desire. These were short studies measuring sexual response, not safety or tanning over time.

Crucially, there are no controlled human trials validating its main real-world use, tanning, for either efficacy or safety, and none for weight loss. So the evidence that exists doesn’t actually cover what most people take it for. A related melanocortin agonist, bremelanotide (Vyleesi), did complete full trials and is FDA-approved for acquired, generalized hypoactive sexual desire disorder in premenopausal women, but that is a different, regulated drug and says nothing about the safety of unregulated Melanotan II.

So why grade it “Preliminary human” at all? Because, narrowly, the erectile-response work is small, short, placebo-controlled human testing — genuine early human evidence for one endpoint. The honest caveat is that it does not extend to tanning, weight loss, or long-term safety, which is what people actually buy it for.

Legal and regulatory status

Melanotan II is not approved by the FDA for any use. The FDA treats products marketed for human use as unapproved new drugs and misbranded cosmetics and has issued warning letters to sellers. The UK’s MHRA and Australia’s Therapeutic Goods Administration have both warned the public against it and treat its sale as illegal, and it is widely sold on the gray market. For athletes, Melanotan II is not listed by name on the WADA Prohibited List, but because it has no approval for human therapeutic use anywhere, it plausibly falls under the S0 “non-approved substances” catch-all, which is prohibited at all times; competitors should treat it as banned and check the current list. As of 2026 there is no legal, regulated source for human use.

Safety

This is the heart of the problem. Documented harms in case reports and regulatory warnings include: priapism (painful, prolonged erection that can cause permanent damage), nausea and vomiting, flushing, blood-pressure changes, and rhabdomyolysis (severe muscle breakdown) with kidney injury reported after a large overdose. Of particular concern, Melanotan II stimulates melanocytes, and it does not distinguish normal skin from existing moles: case reports describe darkening and rapid change of existing moles, new atypical moles, and melanomas diagnosed during or shortly after use. These reports show association, not proven cause, but they are a serious signal. Because the drug is unregulated, vials may be contaminated, mislabeled, or wrongly dosed, and injecting or sharing needles adds infection risk.

Bottom line

Melanotan II clearly does something, it tans skin and can trigger erections, but “it works” is not the same as “it is safe or wise.” Its real-world uses are untested in controlled humans, it is unapproved and often illegal, and it carries documented risks including reports of melanoma. The honest read is that the evidence supporting how people actually use it is thin, while the safety signals against it are not.

Evidence grade: Preliminary human.

Melanotan II: It Tans, But It's Unapproved and Carries Real Harms