Short answer: Melanotan II is the research peptide with the most documented problems in people, mostly because it has been widely misused as a “tanning injection.” Early human studies in the 1990s found nausea, facial flushing and unwanted erections. Since then, dermatology journals have published case reports of new and changing moles, melanoma, kidney damage and muscle breakdown in people using it. Case reports cannot prove cause, but they are enough for every major skin-cancer and regulatory body to warn against it. Here is the evidence, sorted by how strong it is.
What Melanotan II is (and its two approved cousins)
Melanotan II is a synthetic, cyclic version of alpha-MSH, the hormone that tells pigment cells to make melanin. It was developed at the University of Arizona in the 1980s and 1990s. Its problem is that it is not selective: it activates several melanocortin receptors, including ones involved in skin pigment (MC1R), appetite and sexual function (MC3R and MC4R). Two related molecules did become medicines, and they show what happens when the target is narrowed:
| Melanotan II | Afamelanotide (Melanotan I) | Bremelanotide | |
|---|---|---|---|
| Status | Not approved anywhere | Approved (Scenesse) for erythropoietic protoporphyria | Approved in the US (Vyleesi) for low sexual desire in women |
| Receptor profile | Broad | Mainly MC1R (pigment) | Mainly MC4R (sexual function) |
| Use | Sold online for “tanning” | Implant, specialist prescription | On-demand injection, prescription |
Bremelanotide is, in fact, a metabolite-derived relative of Melanotan II, and its label still lists nausea as the most common side effect and warns about darkening patches of skin with repeated use. The same signals, in a molecule that was properly tested.
What the early human studies found
Small University of Arizona studies in the 1990s tested Melanotan II in healthy men and in men with erectile dysfunction. Wessells and colleagues reported that it induced erections, and across these studies the recurring side effects were:
- Nausea, sometimes with vomiting, often within an hour.
- Facial flushing.
- Spontaneous erections and stretching or yawning.
- Reduced appetite.
- Darkening of skin and existing moles, which was the original point.
These were small, short studies. They established the immediate effects, not long-term safety.
Moles and melanoma: the main concern
This is why dermatologists are blunt about Melanotan II. Pigment cells are also the cells that become melanoma, and Melanotan II pushes them to grow and produce pigment. Published case reports describe:
- Eruptive moles: many new moles appearing within weeks of starting use.
- Changing moles: existing moles darkening or becoming irregular, including in a teenager with a familial mole syndrome who also used sunbeds (Sivyer, 2012).
- Melanoma diagnosed in people using Melanotan II (for example Hjuler and Lorentzen, 2014).
How to read this: case reports cannot prove that Melanotan II causes melanoma; many users also tan heavily, which is itself a major risk. But darkening hides changes in moles, which makes melanoma harder to spot early. That combination is why the Skin Cancer Foundation and dermatologists warn against it.
Kidney and muscle: the rare serious reports
Less common, but documented: a case of systemic toxicity with rhabdomyolysis, a breakdown of muscle tissue that can damage the kidneys (Nelson et al., 2012), and a report of kidney infarction, where part of the kidney loses its blood supply (Peters et al., 2020). Prolonged, painful erections (priapism) have also been reported. Any of these needs emergency care.
Health Canada, FDA and dermatologists
| Health Canada | Not authorized. Melanotan I and II are named in Health Canada’s April 2026 advisory on unauthorized injectable peptides. Health Canada has not approved any product for tanning. |
|---|---|
| FDA (USA) | Not approved. The FDA has issued warning letters to companies selling it. |
| Dermatology bodies | The Skin Cancer Foundation and dermatologists advise against its use; a self-tanner plus sun protection is the safe way to get colour. |
Frequently asked questions
Cliquez sur une question pour afficher la réponse.
What are the side effects of Melanotan II?
Early human studies found nausea, facial flushing, spontaneous erections and reduced appetite. Case reports also describe new and changing moles, melanoma, rhabdomyolysis and kidney damage in people using it.
Does Melanotan II cause skin cancer?
It has not been proven to cause melanoma, but melanoma has been reported in users, it stimulates the cells melanoma comes from, and darkening makes changing moles harder to spot. Dermatologists advise against it.
Does Melanotan II cause new moles?
Yes, eruptive and darkening moles are among the most frequently reported effects in the medical literature.
Is Melanotan II legal in Canada?
No product is approved for tanning in Canada, and Melanotan II is named in Health Canada’s April 2026 advisory on unauthorized injectable peptides.
What is the difference between Melanotan II and bremelanotide?
Bremelanotide is a related molecule that mainly targets the MC4 receptor and is approved in the US as Vyleesi. Melanotan II acts on several receptors and has never been approved.
Is there a safe alternative for tanning?
Dermatologists recommend self-tanning products, which colour the skin’s surface without stimulating pigment cells, combined with sun protection.
Related reading
- Melanotan 1 vs Melanotan 2
- PT-141 side effects
- Kisspeptin vs HCG vs PT-141
- How to read a peptide COA
- Peptides 101: the plain-English guide
References
- Wessells H, et al. Melanocortin receptor agonists, penile erection, and sexual motivation: human studies with Melanotan II. Int J Impot Res. 2000. PubMed
- Hjuler KF, Lorentzen HF. Melanoma associated with the use of melanotan-II. Dermatology. 2014. PubMed
- Nelson ME, et al. Melanotan II injection resulting in systemic toxicity and rhabdomyolysis. Clin Toxicol. 2012. PubMed
- Peters B, et al. Melanotan II: a possible cause of renal infarction. 2020. PubMed
- Sivyer GW. Changes in melanocytic lesions after Melanotan injections and sunbed use in a teenager with FAMMM syndrome. 2012. PubMed
- The Dermatology Digest. Melanotan exposed: facts, fiction, and safety concerns. 2026. Derm Digest
- Health Canada. Think twice before injecting peptides bought online. Public advisory, April 9, 2026. Health Canada
All TrueLabs products are sold for in vitro and laboratory research use only. They are not intended for human or veterinary use, and nothing in this article is medical advice. If you notice a new or changing mole, see a doctor or dermatologist.