PT-141 (bremelanotide) is a melanocortin receptor agonist FDA-approved in 2019 as Vyleesi for hypoactive sexual desire disorder (HSDD) in premenopausal women — and only for that. It works centrally on brain melanocortin receptors, not on blood flow like Viagra. Widely used off-label in men, but the male evidence is thin, and outside the US it is not an approved medicine.
Melanotan II is a lab-made copy of α-MSH sold online as an injectable "tanning peptide". It is not approved as a medicine anywhere, and peer-reviewed case reports link its use to new and rapidly changing moles, dysplastic nevi and at least one published case of melanoma in situ. The MHRA and Cancer Research UK have publicly advised consumers not to use it.
PT-141 sits at grade A; Melanotan II at grade D. On evidence alone, PT-141 is the safer recommendation. That said, "stronger evidence" doesn't always mean "right for you" — read both pages, then talk to a clinician.
FDA-approved June 2019 as Vyleesi for the as-needed treatment of acquired, generalised HSDD in premenopausal women. Based on the two RECONNECT phase 3 trials (Kingsberg et al. 2019). Effect size is real but modest — a treatment-vs-placebo difference of roughly 0.35 points on the FSFI-Desire scale and 0.27 on FSDS-DAO Q13 — and around 18% of patients on active treatment discontinued because of nausea or other side effects.
Earlier phase 2 work in the 2000s with intranasal bremelanotide in men with ED showed some signal but was discontinued during development because of dose-related transient blood-pressure increases. There are no large modern phase 3 trials in men. Off-label prescribing and very widespread gray-market use exists, but the evidence for the male indication is several rungs below the female one.
Palatin and academic groups have explored melanocortin agonism for reperfusion injury and shock; this remains preclinical / very early clinical and is not a near-term indication.
The desired effect — and the one that drives sales. MT-II does measurably stimulate melanin production. But there are no controlled human trials of MT-II for cosmetic tanning, and the safety trade-off (see below) is the entire issue. This use is not approved by any medicines regulator.
Well-documented as a side effect, and the reason MT-II was historically of interest in sexual-medicine research. The refined, MC4-selective version — PT-141 (bremelanotide) — has since superseded MT-II for this use.
MC4 agonism reduces food intake in animal models. Of historical research interest only; never pursued as a clinical product, and not a reason anyone uses MT-II today.
The dose-limiting side effect is nausea, reported by about 40% of patients in the long-term extension; flushing (~20%) and headache (~12%) are also common. Around 18% of treated patients in RECONNECT discontinued because of adverse events, versus 2% on placebo — a meaningful real-world signal. Bremelanotide transiently increases blood pressure (typically peaking 2–4 hours after a dose) and reduces heart rate, and is therefore contraindicated in uncontrolled hypertension or known cardiovascular disease. With repeat dosing, focal hyperpigmentation — darkening of the face, gums or breasts — can occur, mediated by off-target MC1R activity; it may not fully resolve after stopping. The phase-3 safety dataset is overwhelmingly in women; the safety profile for chronic male use is not characterised at FDA-grade. Not for use in pregnancy.
Melanotan II has the most concerning published safety profile of any peptide on this site. Four signals matter. First, mole and melanoma risk. Multiple peer-reviewed case reports describe new moles erupting, existing moles rapidly darkening or changing shape, and dysplastic nevi developing in MT-II users (Cardones & Grichnik 2009; Cousen et al. 2009; Reid et al. 2012), and at least one published case of melanoma in situ has been associated with MT-II use (Paurobally et al. 2012). Causation in any individual case is not provable, but the mechanism — driving melanocyte activity — is biologically plausible, and the pattern is consistent enough that public-health bodies have warned consumers. Second, systemic toxicity. A 39-year-old man in the Nelson et al. 2012 case presented with sympathomimetic toxicity, tachycardia, hypertension and rhabdomyolysis after a single MT-II injection. A separate case series documents renal infarction associated with MT-II use. Third, common acute effects include nausea, facial flushing, GI upset, blood-pressure changes, yawning and spontaneous erections. Fourth, quality control on the illegal market is absent — vials sold online are unregulated, and purity, identity and sterility are not guaranteed. If you have any moles you are watching, a family history of melanoma, Fitzpatrick I–II skin, or are immunosuppressed, MT-II is a particularly poor choice. Any new or changing mole during or after MT-II use is grounds for immediate dermatology review.
PT-141 sits at grade A; Melanotan II at grade D. On evidence alone, PT-141 is the safer recommendation. That said, "stronger evidence" doesn't always mean "right for you" — read both pages, then talk to a clinician.
Pepwyse comparison pages are generated from the same structured data behind each peptide profile. Want a different head-to-head? Use the compare picker or ask PT-141 directly via the Ask-Peppy button. Not medical advice — see how we grade evidence.