Melanotan II vs Oxytocin

Cosmetic

Hormone

Research Only

FDA Approved

MT-II is a non-selective agonist at all four peripheral melanocortin receptors — MC1R (melanocyte pigmentation), MC3R and MC4R (energy balance and central sexual arousal), and MC5R (exocrine gland function). MC1R activation on melanocytes increases cAMP → PKA → MITF → tyrosinase, driving eumelanin synthesis; UV exposure is generally required to produce visible tanning. MC4R activation in the hypothalamus mediates the prominent sexual arousal and spontaneous erection side effects seen in the original Phase I trials — this observation was the basis for developing the selective C-terminal analog bremelanotide (PT-141, Vyleesi) for female HSDD.

Oxytocin binds oxytocin receptors (OXTR, a Gq-coupled GPCR) on uterine myometrium (triggering contractions) and breast myoepithelial cells (milk let-down). Centrally, OXTR is expressed in amygdala, hypothalamus, nucleus accumbens, and other limbic regions where it modulates social cognition, pair bonding, and stress reactivity. At high IV doses, oxytocin has weak antidiuretic (ADH-like) activity at V2 receptors, which can cause water retention and hyponatremia.

Approximately 1-2 hours

~1-6 minutes (IV); behavioral effects after intranasal dosing reported up to ~30-60 minutes