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Sildenafil is a potent inhibitor of cyclic guanosine monophosphate in the corpus cavernosum and therefore increases the penile response to sexual stimulation. We evaluated the efficacy and safety of sildenafil, administered as needed in two sequential double-blind studies of men with erectile dysfunction of organic, psychogenic, or mixed causes.

In a 24-week dose–response study, 532 men were treated with oral sildenafil (25, 50, or 100 mg) or placebo. In a 12-week, flexible dose-escalation study, 329 different men were treated with sildenafil or placebo, with dose escalation to 100 mg based on efficacy and tolerance. After this dose-escalation study, 225 of the 329 men entered a 32-week, open-label extension study. We assessed efficacy according to the International Index of Erectile Function, a patient log, and a global-efficacy question.

In the dose–response study, increasing …