The origin story is better than the effect size, and the effect size is real. In the 1990s a peptide called Melanotan II was being studied to darken skin without sunlight. It did that. It also, in a University of Arizona study, produced erections in men who were not expecting any. Eight of ten, tip rigidity above 80 percent for 38 minutes against 3 minutes on placebo. One of the chemists, self-experimenting, once doubled his own dose by mistake and spent eight hours with an erection he had not planned.
Palatin took the accident, trimmed it to a cyclic heptapeptide called PT-141, renamed it bremelanotide, and eventually got Vyleesi approved in 2019. The receptor doing the work is MC4R, the same melanocortin plumbing that ties appetite, pigment, and arousal together in one untidy knot.
Wessells and colleagues (1998) reported clinically apparent erections in 8 of 10 men given the alpha-MSH analog, with the 38-versus-3-minute rigidity difference. A 2000 follow-up found the effect was not limited to psychogenic cases and noted a desire signal.
What the headline inflatedNothing to inflate here. The lineage from tanning peptide to MC4R agonist to approved drug is exactly as advertised.
The two RECONNECT trials (integrated, 1,247 women in the safety population, 24 weeks) hit both co-primary endpoints. Desire rose 0.35 and distress fell 0.33 against placebo, both highly significant. The desire effect size was 0.39, small by convention. FDA figures track this at roughly 25 percent versus 17 percent for a meaningful desire jump.
What the headline inflatedA real, replicated, statistically clean result. The word to keep in mind is small.
The indication is narrow, premenopausal acquired generalized hypoactive sexual desire disorder with distress. Not approved for men.
What the headline inflatedThe co-primaries were desire and distress scores. The count of satisfying sexual events did not move (p around 0.63). Nausea hit 40 percent versus 1.3 percent on placebo. Placebo response ran near 35 percent, and study withdrawal was lopsided (about 42 percent on drug versus 16 percent on placebo in one trial). Modest and real, not a superpower.
The approved product is a fixed 1.75 mg subcutaneous autoinjector, capped at one dose in 24 hours and eight in a month, with instructions to stop at eight weeks if nothing changes. Those caps are toxicity limits, not marketing caution. Every dose transiently raises blood pressure and lowers heart rate, so the label contraindicates it in uncontrolled hypertension or known heart disease. Focal darkening of skin and gums (leftover MC1R activity from the tanning-peptide parent) runs about 1 percent at the labeled cap, climbs sharply with more frequent use, and does not always fade after stopping.
What the headline inflatedThe internet sells the same sequence as unmetered vials and as compounded nasal spray. The nasal route is the exact formulation the FDA halted in 2007 for raising blood pressure, before the drug was ever approved. Same amino acids, but the pen and the powder are not the same product, and the two things the FDA actually controlled, a fixed subcutaneous dose and a hard cap on frequency, are the first things the grey market drops.
A tanning study wandered into the reward system and came back with a licensed drug. That is the whole delight of it.
The mechanism is real, the approval is real, and the benefit is the size of a decent night's sleep, not a transformation.
The version the internet sells is the one the FDA already sent back.
Sources
Phase 3 primary: Kingsberg SA et al. Bremelanotide for HSDD, two randomized phase 3 trials. Obstet Gynecol. 2019;134(5):899-908. PMC6819021 (open access, full text retrieved).
Origin: Wessells H et al. J Urol. 1998;160(2):389-393. PubMed 9679884.
Safety extension: Simon JA et al. Obstet Gynecol. 2019;134(5):909-917.
Approval: FDA, 21 Jun 2019 (first-in-class; approval held by AMAG). Drugs.com approval history.
Label (dosing and safety): Vyleesi (bremelanotide) Prescribing Information, Cosette Pharmaceuticals. One dose per 24 hours, eight per month; transient BP increase and HR decrease; focal hyperpigmentation; nausea 40 percent. vyleesipro.com.
Development history: Melanotan II origin; intranasal program halted by the FDA in 2007 for raised blood pressure; ownership Palatin to King to AMAG to Cosette (2024). Bremelanotide, development history.
Thread: @superpower, 16 Sep 2026.