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α-MSH Analogue · Melanocortin Cyclic Heptapeptide

Melanotan II

MT-II · "Barbie Drug" · Cyclic α-MSH Analogue

"The original melanocortin peptide — discovered when a researcher accidentally injected himself with twice the intended dose and spent eight hours explaining a spontaneous erection to his colleagues. Everything about Melanotan II has been accidental, unauthorised, and fascinating ever since."

Type
Cyclic heptapeptide · α-MSH analogue
Receptor profile
Non-selective: MC1R, MC3R, MC4R, MC5R
Status
UK: not illegal to buy or possess · WADA: not specifically listed · US FDA: removed from Cat 2 Apr 2026 · PCAC review by Feb 2027 · not approved anywhere as medicine
Primary uses
Tanning · sexual function · appetite
Protocol summary
Loading dose
0.25–0.5 mg/day SubQ
Route
SubQ on alternate days
Cycle
Loading then maintenance every few days
Community-reported
0.25–1.0 mg SubQ · titrate slowly
Start very low for nausea/BP tolerance; see safety section before use
How we read the evidence
Unapproved in every jurisdiction · documented melanoma case reports during/after use · rhabdomyolysis at overdose · vendor purity averages well below labelled · this is one of the highest-risk peptides on the platform
Animal evidence

Preclinical work characterised MT-2 as a cyclic, less-selective melanocortin agonist (binds MC1R, MC3R, MC4R, MC5R) — broader receptor spread than MT-1's primarily MC1R selectivity. Animal studies established the tanning effect (MC1R) but also the appetite suppression and erectile-effect signal (central MC4R) that distinguish MT-2 from MT-1. The same broader receptor activation that produces the sexual and weight effects also produces the systemic side effect profile.

Community & clinical practice

Community protocols typically use 0.25–0.5 mg SubQ on alternate days during a loading phase, then maintenance dosing every few days once tan is established. Acute side effects (peak 30–90 minutes post-injection) — nausea, flushing, dizziness, yawning, spontaneous erections in men — are near-universal during loading. Mole darkening (often persistent), new mole formation (can be permanent), nail melanonychia, freckle deepening are commonly reported. Injection-site hyperpigmentation. Rhabdomyolysis case at 6 mg dose (Nelson et al. 2012 — ~12× the standard starting dose). Ischemic priapism after a single 2 mg SubQ dose documented in peer-reviewed case report.

Human trial data

Limited human trials. Dorr et al. 1996 (Life Sciences) Phase 1 pilot in healthy subjects established the basic dose-response and side-effect profile. Wessells et al. 1998 and 2000 (Urology) demonstrated erectile-response signal at studied doses — work that ultimately led to the development of bremelanotide (MC4R-selective, FDA-approved as Vyleesi for HSDD) rather than MT-2 itself. Dorr et al. 2004 examined MT-II + UV pigmentation effects. No Phase 2/3 development was pursued; pharma deliberately moved on to receptor-selective descendants because MT-2's broad melanocortin activation profile was not a viable drug-development path.

Regulatory status

Not approved anywhere — US, UK, EU, Australia all unapproved. WADA-banned. Vendor quality is the largest sourcing issue: a 2015 analysis found some products contained only 43% of labelled MT-2 content. Documented serious adverse events: at least 4–5 melanoma case reports during or after MT-2 use (Brennan et al. 2017 review; Ong & Bowling 2012; Hjuler & Lorentzen 2014; Cardones & Grichnik 2009; Cousen 2009 BJD on MT-1; oral mucosal melanoma case from MT-II nasal spray, ScienceDirect 2025). Whether MT-2 directly causes melanoma vs simply revealing pre-existing lesions through pigment changes is genuinely unclear — but the case-report cluster is meaningful.

Convergence

Melanotan-2 is one of the highest-risk peptides on this platform. Pharma deliberately abandoned it for receptor-selective descendants (bremelanotide for sexual dysfunction; afamelanotide for EPP) because the broad melanocortin activation profile was not viable. The evidence picture: documented melanoma case reports, ischemic priapism case, rhabdomyolysis case, severe vendor quality issues, no regulatory approval anywhere, and no formal long-term safety data. Pep IQ does not endorse cosmetic MT-2 use. If sexual function is the goal, bremelanotide (Vyleesi) is FDA-approved and MC4R-selective — that's the right molecular tool. If photoprotection is the goal, afamelanotide (Scenesse) is the right tool. MT-2 is the unselective version of both, and that's why it's the riskier choice.

Origin & Background

The accidental sex drug

Melanotan II was developed at the University of Arizona in the 1980s and 1990s as part of an effort to create a safe tanning agent — a peptide that would stimulate melanin production without UV radiation, potentially reducing skin cancer risk. Researchers Mac Hadley and Victor Hruby synthesised a cyclic analogue of α-melanocyte stimulating hormone (α-MSH) that was more potent and more stable than the natural peptide.

The defining moment in its history came when one of the researchers self-injected the compound at twice the intended dose and experienced an eight-hour erection alongside nausea and vomiting. This accidental discovery redirected the research programme — one branch continued as the tanning peptide (eventually becoming afamelanotide, which is FDA-approved under the name Scenesse for erythropoietic protoporphyria) and another became PT-141/bremelanotide (FDA-approved as Vyleesi for HSDD).

Melanotan II itself was never developed into an approved drug — Clinuvel Pharmaceuticals abandoned this pursuit due to regulatory concerns and the non-selective receptor profile. Instead, it has circulated as an unregulated compound sold online and through gym networks for decades. It became known as the "Barbie drug" in the UK press due to its tanning and appetite-suppressing effects. Regulatory agencies in multiple countries have issued warnings against its use.

Critical regulatory status: Melanotan II is not approved anywhere. It is not the same as afamelanotide (Scenesse) or bremelanotide (Vyleesi) — both of which are FDA-approved products from the same research lineage. Melanotan II is sold unregulated, unverified, and untested for purity or dosing accuracy. The compounds sold online are frequently mislabelled, contaminated, or of unknown composition.

Science & Mechanism

Non-selective — all five receptors

Mechanism of Action

1
MC1R — tanning: Non-selective agonist of all five melanocortin receptors. MC1R activation in melanocytes stimulates eumelanin synthesis, producing skin darkening. Effect begins within 5–10 doses. Exaggerates UV-mediated tanning when combined with sun exposure.
2
MC3R/MC4R — sexual arousal: Central nervous system activation of MC3R and MC4R in the hypothalamus and limbic system drives dopaminergic sexual arousal pathways — the same mechanism as PT-141/bremelanotide. Spontaneous erections in men within 1–5 hours of injection are a consistent side effect.
3
MC4R — appetite suppression: MC4R activation suppresses appetite and reduces food intake. This "side effect" is frequently welcomed by users seeking body composition benefits alongside tanning.
4
Non-selectivity — the problem: Unlike PT-141 (which is refined to target MC3R/MC4R predominantly), Melanotan II activates all five MCRs non-selectively. MC5R activation causes flushing, nausea, and yawning. The full receptor profile produces a broader and less predictable side effect profile than any approved melanocortin agent.
5
Blood-brain barrier penetration: Melanotan II crosses the blood-brain barrier readily — contributing to its central sexual and appetite effects, but also creating more unpredictable CNS effects than its approved derivatives.
Benefits & Evidence

What the data shows

🌞
Skin tanning without UV
MC1R activation stimulates eumelanin synthesis — producing genuine skin darkening within 5–10 doses, exaggerated by concurrent UV exposure. The tanning effect is consistent and well-documented in early clinical trials. Trials were stopped due to regulatory concerns about promoting tanning behaviour rather than efficacy questions.
● Moderate — early clinical trials, discontinued
⚡
Erectile function and sexual arousal
Phase I/II trials showed spontaneous erections in 80–90% of men; significant erectile response in ED patients. The same mechanism as PT-141 (bremelanotide) which is FDA-approved for this application. The evidence for the sexual function effect is real — but PT-141 delivers it more safely and with regulatory oversight.
● Moderate — Phase I/II data (same mechanism as FDA-approved PT-141)
🍽️
Appetite suppression and weight
MC4R-mediated appetite suppression is a consistent reported effect — users note significant reduction in hunger. This is the same receptor that setmelanotide (Imcivree) targets for approved treatment of genetic obesity. The effect is real but uncharacterised for dosing and safety in the unregulated context.
● Limited — observed but uncontrolled in humans
Things to know

Risks & considerations

🚨
The most concerning safety profile in this book. Multiple regulatory agencies have issued warnings. Five case reports of melanoma in users. Severe overdose cases including rhabdomyolysis, priapism requiring surgery, and systemic toxicity. The unregulated supply chain adds contamination risk to an already serious pharmacological risk profile.
Moderate
Nausea, flushing, fatigue, yawning — universal early side effects from non-selective MCR activation. Usually reduce with continued use. Significant on first doses.
Moderate
Spontaneous erections / priapism — penile erections within 1–5 hours of injection are a consistent effect in men. Rare but severe priapism cases have required surgical intervention — one case after 6mg (3x starting dose) required ICU admission.
Serious
Mole changes and melanocytic naevi — reversible darkening of moles and freckles is common. New moles and atypical melanocytic naevi have been reported. Any change in existing moles requires dermatological evaluation before continuing use.
Serious
Melanoma association — at least five published case reports of melanoma in Melanotan II users, though all had additional risk factors (fair skin, sun beds, family history). A 2013 review found no conclusive causal evidence, and a 2021 review suggested the association may reflect greater UV exposure in users rather than direct melanogenesis-driven carcinogenesis. The question is not resolved. Anyone with fair skin, a history of unusual moles, or family history of melanoma should not use this compound.
Serious
Systemic toxicity at overdose — one published case of 6mg injection (3x recommended dose) produced sympathomimetic toxicity, rhabdomyolysis (CPK 17,773 IU/L), renal dysfunction, and required 3 days ICU admission. The unregulated supply means dose accuracy is unknown.
Serious
Contaminated supply — sold as research compound with no manufacturing oversight. Studies of online MT-II products have found contamination, mislabelling, and concentration inaccuracies. What you order is not necessarily what you inject.

⚠ Key Warnings

If you want skin tanning: use afamelanotide (Scenesse) prescribed for erythropoietic protoporphyria where available, or accept the UV risks of natural tanning. Melanotan II is not a safe tanning solution.
If you want the sexual function effects: PT-141 (bremelanotide/Vyleesi) is FDA-approved, provides identical MC3R/MC4R activation, with verified dosing and without the tanning and melanoma risks.
Any change in existing moles during Melanotan II use — see a dermatologist immediately and discontinue until cleared.
Fair skin (Fitzpatrick I/II), personal or family history of melanoma, or history of unusual moles are absolute contraindications.
Never exceed 0.025mg/kg starting dose. The systemic toxicity case occurred at 6mg — 3x the starting dose in a 65kg person. The unregulated supply makes dose verification impossible.