Melanotan II monograph

Overview

Melanotan II is an unapproved synthetic melanocortin analog originally studied for tanning and sexual-function effects. In humans it can increase pigmentation and can provoke sexual arousal/erection, but the safety profile is not clean and the evidence base is limited compared with approved melanocortin drugs. It is commonly used outside medicine as a tanning/bodybuilding-adjacent gray-market peptide, which is exactly where dosing and product-quality problems become a real issue.[^1]

Pharmacokinetics & Mechanism

• Class: Synthetic melanocortin receptor agonist; cyclic truncated α-MSH analogue / peptide
• Mechanism of action: Melanotan II is a non-selective melanocortin receptor agonist. It activates melanocortin pathways involved in melanogenesis and central sexual behavior/erectile responses; it was described as a cyclic truncated peptide with prolonged action and enzymatic resistance. Human studies showed erection and increased sexual desire without sexual stimulation, consistent with central melanocortin signaling rather than direct androgenic action.
• Target(s): Primarily melanocortin receptors, especially non-selective activation across the melanocortin receptor family; the literature links the clinical effects to MCR-mediated pathways rather than a single receptor subtype. Functionally relevant downstream effects include stimulation of melanogenesis and central sexual-motivation/erectile pathways. Exact receptor selectivity and human pathway contribution are not well established in routine clinical use.
• Route(s) of administration: Subcutaneous injection is the common reported route in clinical reports and community use. Human case literature also reports abdominal subcutaneous injection. No approved oral, intranasal, or topical route is established for standard medical use.
• Onset: Not well established as a formal PK parameter in humans. In the erectile-function study, penile rigidity was monitored over 6 hours and responses occurred during that observation window, while community users usually report effects within hours after injection. For tanning effects, onset is typically described qualitatively rather than with robust human PK timing data.
• Half-life: Human half-life is not well established in the accessible sources and appears under-characterized in the peer-reviewed literature. It is commonly described online as short, roughly on the order of a few hours, but I would treat that as anecdotal unless a specific PK study is available. No reliable evidence supports a long-acting DAC/extended variant for Melanotan II itself; that concept belongs to different peptide formats, not standard MT-II.
• Metabolism / clearance: Not well established in humans. As a peptide, it is expected to undergo proteolytic degradation and renal/hepatic clearance of peptide fragments, but the specific metabolic pathways, active metabolites, and clearance kinetics are not well defined in the sources reviewed. The literature emphasizes that it is enzymatically resistant relative to native peptides, not that it has a clinically mapped clearance pathway.