Melanotan II

1. 01Bloodstream

   Injected under the skin and carried in the blood

   In the studies, doctors gave it as a small injection under the skin. From there it reaches the bloodstream and can act all over the body, which is why it can affect both skin colour and the brain.

   For experts

   In the human studies MT-II was given subcutaneously, and effects (nausea, yawning and stretching, intermittent spontaneous erections over 1-5 hours, later skin darkening) followed dosing, indicating systemic exposure. The lactam ring, D-Phe7 and Nle4 came from a design programme aimed at high potency; in frog and lizard skin bioassays the 23-membered-ring analogues showed prolonged residual activity. No published human pharmacokinetic study (absorption, half-life, clearance) was found.[src][src]

2. 02Skin

   Switches on pigment cells in the skin

   It copies a natural hormone called alpha-MSH. In the skin it fits receptors on pigment cells, which then make more dark pigment (melanin). In a small human study this darkened skin after just a few injections.

   For experts

   MT-II activates MC1R on melanocytes, increasing eumelanin synthesis. In the pilot phase 1 study, two of three men had increased facial, upper-body and buttock pigmentation, measured by reflectance, after a short course of injections. The pigment change is not a substitute for sun protection: the TGA states it does not protect against UV in the way a suitable sunscreen does.[src][src][src]

3. 03Brain

   Brain appetite circuits (shown in animals only)

   In mice, putting the peptide straight into the brain made them eat less. It works on brain receptors that normally help signal that the body has had enough food. This has only been shown in animals, and it is not how people use it.

   For experts

   Intracerebroventricular MT-II, a potent agonist at neural MC3R and MC4R, inhibited feeding in four mouse hyperphagia models (fasted, ob/ob, agouti A(Y), and neuropeptide-Y-injected mice); co-administration of the antagonist SHU9119 blocked the effect. This is animal-only evidence from central injection. It does not establish an effect on body weight in humans, and MT-II is not an approved or trialled weight-loss drug.[src]

4. 04Brain

   Brain pathways for sexual response (small human studies)

   In small studies, men given the peptide by injection had erections without needing physical stimulation, and often reported more sexual desire. Scientists think this starts in the brain, not in the penis itself.

   For experts

   In a double-blind, placebo-controlled crossover study of 10 men with psychogenic erectile dysfunction, 8 of 10 developed clinically apparent erections; mean duration of tip rigidity above 80% was 38.0 minutes with MT-II versus 3.0 with placebo (p=0.0045). In men with organic risk factors, erections were reported after 12 of 19 injections versus 1 of 21 placebo doses, and desire scores were higher after MT-II. The authors describe MT-II as a centrally acting melanocortin agonist; these studies did not isolate which receptor subtype drives the effect in humans.[src][src][src]

5. 05Gut

   Broad receptor activation and common side effects

   Because it switches on several kinds of melanocortin receptors, not just one, it causes side effects such as nausea, yawning, stretching and lower appetite. These were common in the studies.

   For experts

   MT-II is non-selective across melanocortin receptors. Nausea (severe after 4 of 19 injections in one crossover study), stretching-and-yawning, decreased appetite, fatigue and somnolence (WHO grade II in one volunteer at the highest dose) were reported in the clinical studies; nausea, yawning, stretching and reduced appetite occurred more often than with placebo.[src][src][src][src]

6. 06Skin

   Moles and melanoma: reports, not proof

   Doctors have reported people getting new or changing moles after using unregulated melanotan products, and a few melanomas. These are case reports, so they cannot prove the peptide caused the cancers. Regulators warn people about this.

   For experts

   Case reports describe multiple new atypical naevi within a week of two melanotan injections, a melanoma in a user, and a mucosal melanoma after nasal-spray use. Whether chronic MC1R stimulation of melanocytes causes malignant change has not been established in controlled studies, and single case reports cannot establish causation or rule out other factors such as sun exposure. FDA's compounding safety page lists melanoma among serious adverse events in published case reports.[src][src][src][src]

7. 07Kidneys

   Serious reactions in users of unregulated products

   Some people who used unregulated products ended up in hospital with a racing heart, muscle damage and kidney problems. These are reports about single patients, and what was really in the products was often unknown.

   For experts

   Case reports include a sympathomimetic toxidrome with rhabdomyolysis and kidney injury after injection of a product confirmed by mass spectrometry to be MT-II, renal infarction, posterior reversible encephalopathy syndrome, and priapism requiring aspiration and irrigation of the penis. Mechanisms are not established; for the renal infarction, the authors suggested a thrombotic effect or direct kidney toxicity. Incidence cannot be estimated from case reports.[src][src][src][src]

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