Melanotan II

Melanotan II (MT-II) is a non-selective synthetic analogue of alpha-melanocyte stimulating hormone (α-MSH), a naturally occurring melanocortin peptide. Developed at the University of Arizona as part of a tanning agent research program, MT-II was found to have potent effects on skin pigmentation, libido, and appetite suppression — effects that led to both significant research interest and widespread unregulated use. It is the parent compound from which PT-141 (bremelanotide) was derived. MT-II stimulates broader melanocortin receptor activity than PT-141, which accounts for its tanning effects (MC1R) and greater side effect potential.

MT-II activates multiple melanocortin receptor subtypes simultaneously: MC1R (melanocytes — responsible for the tanning/pigmentation effect), MC3R (limbic system — reward, appetite, cardiovascular tone), MC4R (hypothalamus — sexual arousal, appetite suppression, energy balance), and MC5R (exocrine glands). MC1R activation triggers eumelanin production in skin melanocytes, producing a tan even without UV exposure. MC4R activation drives the potent libido and appetite suppression effects — the same central mechanism as PT-141 but with full rather than selective receptor binding. The non-selective nature of MT-II compared to PT-141 means it produces a broader range of effects (tanning, libido, anorexia) along with a correspondingly broader side effect profile.

Melanotan II was originally developed at the University of Arizona (Dr. Victor Hruby) as a synthetic melanotropin for skin protection research. Pilot clinical studies at the University of Arizona demonstrated tan induction without UV exposure, motivating interest in photoprotection applications. Phase I clinical trials confirmed dose-dependent tanning and sexual arousal effects. Subsequent research focused on MT-II's appetite suppression via MC4R (relevant to obesity pharmacology). The isolated sexual arousal activity of MT-II led directly to the development of PT-141 (bremelanotide) as a selective compound. Dermatological safety concerns emerged from case reports of atypical nevi changes in users — these reports influenced the FDA's decision to pursue selective MCR agonists (PT-141) rather than full MCR agonists for approved therapeutics.

Tanning Loading Protocol: Start at 0.1 mg SC at night, increase by 0.1 mg every 3 nights to 0.5 mg. Use 2–3 times weekly with moderate UV exposure for 3–4 weeks. Maintenance: 0.25–0.5 mg once or twice weekly. Caution: Regular full-body skin inspection by a dermatologist is strongly recommended for anyone using MT-II due to mole changes.

Melanotan II has a more significant side effect profile than PT-141 due to its non-selective melanocortin activation. Nausea and facial flushing are nearly universal, particularly at higher doses or during initial use — typically peaking 30–60 minutes post-injection. Spontaneous erections in men (often unwanted and prolonged) are a well-documented effect of MC4R activation. Extreme appetite suppression can occur, occasionally severe enough to make eating difficult. Darkening of existing moles and the development of new moles or freckles is documented and considered a significant safety concern, as MC1R activation may promote melanocyte proliferation in atypical nevi — this is the primary safety concern driving dermatologists' caution about MT-II. Changes in blood pressure have been reported. Fatigue, yawning, and a temporary disoriented feeling post-injection are commonly described. Use in individuals with a history of melanoma or dysplastic nevi is strongly inadvisable.

Store lyophilized MT-II at -20°C for long-term storage. Short-term storage at 2–8°C is acceptable for up to 3 months. Reconstitute with bacteriostatic water; a 10 mg vial with 2 mL BAC water yields 5,000 mcg/mL. Store reconstituted solution at 2–8°C and use within 28 days. Protect from light — melanocortin peptides can degrade with UV exposure. The peptide is sensitive to heat — never leave in a warm environment.