The melanotan peptides (1 through 5) all mimic melanocyte-stimulating hormone and cause skin darkening, but melanotan 1 does not cross the blood-brain barrier (only tanning), whereas melanotan 2-5 cross it and additionally increase mood and libido and decrease appetite; PT-141 (the FDA-approved drug Vyleesi) targets this system and is approved for premenopausal hypoactive sexual desire in women but is used off-label in men.