• Katrina Wilcox Hagberg, Hozefa A Divan, Rebecca Persson, J Curtis Nickel, and Susan S Jick.
• Boston Collaborative Drug Surveillance Program, Boston University School of Public Health, Lexington, MA 02421, USA khagberg@bu.edu.
• BMJ. 2016 Sep 22; 354: i4823.

Objective To estimate the risk of erectile dysfunction in men who used 5-α reductase inhibitors to treat benign prostatic hyperplasia or alopecia.Design Cohort studies with nested case-control analyses.Setting UK Clinical Practice Research Datalink.Population Two populations of men free of risk factors for erectile dysfunction and other sexual dysfunction or its treatment: men aged 40 or more with benign prostatic hyperplasia who received a prescription for a 5-α reductase inhibitor (finasteride or dutasteride) or α blocker, or both, and men aged 18-59 with alopecia.Exposures In the benign prostatic hyperplasia study, exposures were classified as 5-α reductase inhibitors only, 5-α reductase inhibitors+α blockers, or α blockers only. In the alopecia study, exposures were finasteride 1 mg or no treatment.Main Outcome Measures Cases were men with a diagnosis of erectile dysfunction or treatment (procedure or prescription for a phosphodiesterase type 5 inhibitor) during follow-up. We calculated incidence rates and adjusted incidence rate ratios with 95% confidence intervals. We also conducted nested case-control analyses to control for major confounders, and calculated adjusted odds ratios with 95% confidence intervals.Results In the population with benign prostatic hyperplasia (n=71 849), the risk of erectile dysfunction was not increased with use of 5-α reductase inhibitors only (incidence rate ratio 0.92, 95% confidence interval 0.85 to 0.99; odds ratio 0.94, 95% confidence interval 0.85 to 1.03) or 5-α reductase inhibitors+α blocker (1.09, 0.99 to 1.21, 0.92; 0.80 to 1.06) compared with α blockers only, and remained null regardless of number of prescriptions or timing of use. The risk of erectile dysfunction increased with longer duration of benign prostatic hyperplasia, regardless of exposure. For the alopecia population (n=12 346), the risk of erectile dysfunction was not increased for users of finasteride 1 mg compared with unexposed men with alopecia (1.03, 0.73 to 1.44; 0.95, 0.64 to 1.41).Conclusion 5-α reductase inhibitors do not seem to significantly increase the risk of incident erectile dysfunction, regardless of indication for use. Risk of erectile dysfunction increased with longer duration of benign prostatic hyperplasia.Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

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