Approximately 9 percent of men have some degree of erectile dysfunction. Sildenafil (Viagra), the first oral drug marketed for the treatment of erectile dysfunction, relaxes smooth muscle in the corpora cavernosa, enabling erection during arousal. To evaluate the efficacy of sildenafil, Burls and colleagues reviewed published randomized, doubleblind, controlled trials, reviewed key journals, and contacted experts on erectile dysfunction, the drug's manufacturer, and the U.S. Food and Drug Administration.

The 21 studies identified involved approximately 4,000 men, all of whom were in stable heterosexual relationships and reported erectile dysfunction of at least six months' duration; 3,000 of these men received sildenafil. Extensive exclusion criteria included elevated prolactin or low free testosterone levels, deformity, uncontrolled major psychiatric disorders, and a history of major renal, hepatic, or hematologic disorder. More than 80 percent of the men completed the trials. The primary outcome was sexual function as measured by the standardized International Index of Erectile Function questionnaire.

The 16 trials with sexual function as primary outcome showed significant improvement in men who were given sildenafil. Improvement increased with increasing dose (range: 25 to 100 mg). Insufficient data were found to draw conclusions about added benefit from higher doses (200 mg rather than 100 mg). Based on the trials, men with erectile dysfunction were 3.6 times more likely to improve with sildenafil than with placebo. The number needed to treat for one additional man to improve was estimated at two.

Most men in the trials were white; therefore, analyses by race were not possible. Sildenafil was effective in elderly men. Efficacy was reduced in men who had undergone radical prostatectomy.

The authors concluded that sildenafil is an effective treatment, based on consistent results from a number of trials.