Melanotan II: The Tan Peptide With A Melanoma Signal

The short version

Melanotan II is a lab-made peptide that tans skin without sun. It works by switching on a receptor in skin cells that normally responds to UV light, telling them to make more pigment. People also use it because the same receptor system, active in the brain, lowers appetite and raises sex drive.

It has never been approved as a medicine anywhere. It is sold as a research chemical and typically self-injected, with no doctor involved and no quality control on what is actually in the vial. The safety record is not clean. Published case reports link it to new and changing moles, kidney injury, priapism, and — in documented cases — melanoma. This page states the pigmentation and appetite findings plainly. It states the risk record just as plainly, in the same amount of detail.

What it is

Melanotan II is a cyclic, lactam-bridged heptapeptide analog of alpha-melanocyte-stimulating hormone (alpha-MSH). Its sequence — Ac-Nle4-cyclo[Asp5-His6-D-Phe7-Arg8-Trp9-Lys10]-NH2 — is a truncated, cyclized, D-Phe-substituted derivative of the core alpha-MSH fragment. Researchers Hruby and Hadley designed it at the University of Arizona in the late 1980s, engineering it for superpotent, enzymatically resistant melanotropic activity: the cyclic structure and unnatural amino-acid substitution resist the enzymes that would otherwise break down the natural hormone in minutes. Molecular formula C50H69N15O9.

Melanotan II is distinct from two peptides it is often confused with. Afamelanotide (Melanotan I, the linear precursor) is separately FDA-approved for a rare light-sensitivity condition. Bremelanotide (PT-141), developed from the same lineage, is FDA-approved for a sexual-dysfunction indication ^[4]. Neither approval applies to Melanotan II itself, which remains unapproved for any use.

How it works

Melanotan II is a non-selective agonist across the melanocortin receptor family, MC1R through MC5R. Activating MC1R on melanocytes raises intracellular cAMP and drives a signaling cascade (PKA-CREB-MITF) that increases the enzyme tyrosinase and shifts pigment production toward eumelanin — the dark pigment — without needing UV exposure to trigger it. That is the mechanical basis of the tan.

The same molecule also acts centrally. MC4R and MC3R activation in the hypothalamus and mesolimbic reward system, documented in rodent and early human studies, drives the appetite-suppressing and sexual-motivation effects users report. This is not a side reaction — it is the same receptor family doing what it does in the brain, not just the skin. MC5R activity in exocrine and sebaceous glands rounds out the receptor targets, with effects less studied in humans.

What the research shows

Pigmentation, without sun. In a pilot Phase I study of three healthy male volunteers, subcutaneous Melanotan II escalated to 0.025-0.03 mg/kg every other weekday increased facial, upper-body, and buttock pigmentation in two of three subjects after only five low doses. Side effects included spontaneous erections lasting one to five hours and mild nausea ^[6].

Erectile function. In a double-blind, placebo-controlled crossover study of 10 men with psychogenic erectile dysfunction, subcutaneous Melanotan II (0.025 mg/kg) produced clinically apparent erections in 8 of 10 men. Mean duration of strong rigidity was 38.0 minutes versus 3.0 minutes on placebo (p=0.0045), with transient, untreated nausea, stretching, and yawning ^[5].

Appetite. In male mice, direct microinjection of Melanotan II into the brain's nucleus accumbens significantly decreased food consumption and food-motivated behavior, without producing an aversion response or changing metabolic rate — evidence the appetite effect is a genuine motivational change, not sickness ^[2].

Oral pigmentation, 2026. A recent case report documents a man who self-administered Melanotan II (400 micrograms subcutaneously every other day for 64 days) and developed brown pigmentation on his gum and cheek tissue. The pigmentation was reversible — cheek tissue began fading within 28 days of stopping, though gum pigmentation persisted at reduced intensity three months later ^[1].

Kidney injury. A nephrology case report and literature review describes renal infarction most likely attributable to Melanotan II use, noting that MT-II-linked rhabdomyolysis and kidney failure have been described previously, with thrombotic and direct toxic mechanisms both proposed ^[3].

Lineage and marketing. A historical review traces Melanotan I and Melanotan II through clinical testing and patent history, and a 2025 analysis of online marketing highlights the gap between how melanotan is promoted on social media — as the 'Barbie drug' — and its documented, unapproved-drug risk profile ^[4][7].

Reported effects, cautions & safety

Community-reported effects are anecdotal, not clinical evidence, and none of it comes with a verified dose.

Users most often report a rapid, deep tan achieved with far less sun than they would otherwise need — the reason most people seek it out. Set against that: many describe the tan coming in blotchy or unevenly, with an unnaturally long-lasting color, sometimes with an orange or grey cast. Nausea is one of the most consistently reported effects, usually strongest in the first hour after a dose and easing with continued use. Facial flushing, spontaneous stretching and yawning, and a run-down 'melanotan flu' in the early days are all frequently mentioned. Reduced appetite is near-universal and often shows up from the first dose; some treat it as a bonus, others as unwelcome. Men commonly report a sudden libido increase and spontaneous, sometimes inconveniently timed, erections.

The report that matters most for safety: users very commonly describe their existing moles and freckles darkening, and a smaller but recurring group describes brand-new moles appearing during use — sometimes several at once. This is frequently what prompts people to see a dermatologist, and it lines up directly with the published case-report literature below.

Cited safety cautions, in full:

New, changing, or darkening moles, and melanoma. Because Melanotan II drives melanocyte activity across the whole skin, published case reports describe eruptive new nevi, atypical nevi, and darkening of existing moles during use. Multiple case reports go further and document melanoma, including melanoma in situ, arising in people who used melanotan. Dermoscopy studies confirm measurable changes to pigmented lesions during use. Any new or changing mole during or after use warrants prompt dermatological assessment — this is the single most serious documented risk associated with this compound.

Rhabdomyolysis and acute kidney injury. A published case links Melanotan II injection to systemic toxicity with rhabdomyolysis, and a separate case with literature review documents renal infarction ^[3]. The mechanism is not fully understood and may relate to the peptide's effect on blood vessels.

Priapism. Because melanocortin agonism promotes erections, multiple case reports describe priapism — a prolonged, painful erection — following melanotan use, including after apparent overdose. Priapism is a urological emergency; delayed treatment can cause permanent damage.

Posterior reversible encephalopathy syndrome (PRES). A case report describes this brain-swelling condition, presenting with headache, seizure, and visual disturbance, in association with melanotan use — consistent with the compound's known effects on blood pressure.

Cardiovascular and gastrointestinal effects. Preclinical work on alpha-MSH analogs shows melanocortin agonists can raise blood pressure, an effect worsened by impaired nitric-oxide signaling in animal studies. Combined with the very commonly reported nausea, this points to real cardiovascular and gastrointestinal effects that are poorly characterized in humans using unregulated product.

Unregulated product. Analytical studies of melanotan products bought online repeatedly find inaccurate labeling, variable or unverifiable peptide content, and impurities. Melanotan appears in surveys of falsified and black-market injectables. With no quality control, a buyer cannot know the actual identity, dose, purity, or sterility of what is in the vial — a fact that compounds every other risk on this list.

No regulatory approval. Melanotan II has never been approved by the FDA or any other regulator for any use, and it never completed late-phase clinical trials. Regulators including the FDA, Australia's TGA, the UK's MHRA, and Ireland's HPRA have specifically warned against melanotan tanning products. It is a research chemical, not a medicine or a cosmetic.

Not the same as the approved drugs in its family. Melanotan II is sometimes confused with afamelanotide, approved for a rare light-sensitivity disorder, and with bremelanotide (PT-141), approved for a sexual-dysfunction indication ^[4]. Those approvals, and the controlled-trial safety data behind them, do not extend to Melanotan II — a different, unapproved compound used without medical oversight.

Where it fits in Skin & Aesthetics

Melanotan II is the lead compound on this site because it is the most-searched and most-documented of the two — with real efficacy data, a real adverse-event literature, and the widest gap between how it is marketed and what the case reports show. GLOW sits in a different category: a multi-peptide blend built for skin texture and repair rather than pigmentation, with individual-component research but no blend-level human trials. See the side-by-side comparison for how the mechanisms, evidence, and open risks differ between the two.