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Br J Gen Pract. 2001 Dec;51(473):1004-12.

Systematic review of randomised controlled trials of sildenafil (Viagra) in the treatment of male erectile dysfunction.

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Department of Public Health & Epidemiology, Keele University.



Sildenafil (Viagra), a new oral drug for the treatment of erectile dysfunction, was licensed for use across Europe in 1998.


To examine the effectiveness and safety of sildenafil as an oral treatment for erectile dysfunction.


Systematic review and meta-analysis.


All published or unpublished randomised controlled trials comparing sildenafil with a placebo or alternative therapies.


Published studies were sought by computerised searches of electronic databases using the keywords 'sildenafil' and 'Viagra'. A hand search was also done of the British Medical Journal, Lancet, Journal of the American Medical Association, New England Journal of Medicine, British journal of General Practice, Drug, Inpharma and Scrip. An assessment of quality of all identified studies and data extraction was undertaken independently by two researchers. Results were combined in a meta-analysis where appropriate, using RevMan version 3.


Twenty-one trials were identified. All trials showed a statistically significant improvement in erectile or sexual function in patients using sildenafil compared with a placebo. A meta-analysis of 16 trials reporting a global efficacy response showed that men were 3.57 (95% CI = 2.93-4.43) times as likely to have improved erections on sildenafil compared with those on a placebo. The number needed to treat to have one man with improved erections was two. The drug has a relatively safe side-effect profile.


Available research shows that sildenafil is an effective treatment for male erectile dysfunction. Many trial participants had some baseline erectile function and it is probable that in clinical practice, where the erectile function tends to be more impaired, the number needed to treat may be higher.

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