Sexual Function

Definition

Sexual function peptides modulate sexual arousal, libido, and reproductive hormonal signaling through central and peripheral pathways. Unlike PDE5 inhibitors (sildenafil, tadalafil) that work peripherally on penile or clitoral vasodilation, most peptides in this category act centrally on melanocortin receptors or hypothalamic GnRH-pulse generators — meaning they address the motivational and desire aspects of sexual function, not just the physical response. This distinction makes them particularly relevant for patients whose primary complaint involves low desire rather than mechanical erectile or lubrication dysfunction.

Mechanism of Action

PT-141 (Bremelanotide) is a cyclic heptapeptide analog of alpha-MSH (melanocyte-stimulating hormone) that activates MC3R and MC4R melanocortin receptors in the hypothalamus and limbic system. Receptor activation increases dopaminergic tone in mesolimbic pathways and enhances oxytocin signaling, producing central sexual arousal and motivation in both sexes. The effect is dose-dependent and rapid (30–60 minutes to onset). Kisspeptin-10 is the biologically active C-terminal decapeptide of kisspeptin-54, acting on GPR54 (KISS1R) receptors in GnRH neurons. GPR54 activation stimulates pulsatile GnRH release, which drives LH, FSH, and downstream sex hormone production. This makes Kisspeptin relevant for hypothalamic amenorrhea, unexplained infertility, and fertility augmentation.

Regulatory Status

Bremelanotide (Vyleesi, AMAG Pharmaceuticals) is FDA-approved for hypoactive sexual desire disorder (HSDD) in premenopausal women — one of two FDA-approved HSDD treatments. Compounded PT-141 is used off-label in males for erectile dysfunction with a central/desire component; this is not an FDA-approved indication. Kisspeptin-10 is not FDA-approved but has completed Phase I/II clinical trials for hypothalamic amenorrhea and pulsatile LH induction.

Evidence Base

PT-141/Bremelanotide has a robust placebo-controlled RCT evidence base from the RECONNECT trials, which demonstrated statistically significant improvement in satisfying sexual events and decreased distress in women with HSDD. Male PT-141 studies are smaller but show meaningful erectile response in patients who failed PDE5 inhibitors. Kisspeptin's Phase II data from Oxford (Professor Waljit Dhillo's group) demonstrates LH pulse induction in hypothalamic amenorrhea and improved IVF stimulation outcomes.