In the study, 10 men, ages 22 to 59, were each given two injections of varying doses of Melanotan II and two of placebo. Each injection was followed by a 6-hour monitoring period, during which eight men had erections after receiving the drug. The onset of an erection after administration of the drug was about 2 hours, on average. Data were gathered through the men's self-reports and a RigiScan device attached to each man to record penile rigidity and swelling. The results indicated that Melanotan II caused multiple sustained erections that were sufficient for intercourse. No episodes of ejaculation or painful erection were reported, according to the authors. The researchers believe that Melanotan II works by acting on pro-erectile pathways in the central nervous system.