Finasteride 1mg (Propecia) is a drug used to treat alopecia, or male pattern baldness. Results of clinical trials of the 1mg finasteride formulation for alopecia found an increased risk of sexual side effects (1-4), while studies conducted in a clinical setting have suggested that finasteride does not increase the risk of sexual side effects (5-7). A recent review of sexual adverse events from the few published clinical trials reported that the available data is limited and of poor quality and therefore insufficient for establishing the safety profile of finasteride 1 mg for treatment of alopecia (8). Assessment of unintended effects of finasteride 1mg for alopecia is warranted, especially because these drugs are prescribed to healthy young men. To this end, we propose a drug safety study to examine the association between use of finasteride 1mg in men with alopecia and ED in comparison to men with alopecia who do not receive finasteride 1mg.
We will conduct a cohort study with a nested case-control analysis to examine the association between finasteride 1mg use in men with alopecia and erectile dysfunction (ED). We will identify a cohort of men with alopecia, aged 18-59, with no history of sexual dysfunction prior to cohort entry. The incidence of ED among men with exposure to finasteride 1mg (the exposure of interest) will be compared to the incidence of ED among men with no such prescriptions. Crude and adjusted incidence rates (IRs) and 95% confidence intervals (CIs) and incidence rate ratios (IRRs) will be calculated for each exposure category (unexposed and finasteride 1mg exposed). IRs will be calculated as the number of incident events divided by exposed person-time. We will also conduct a nested case-control analysis to control for calendar time, age, and general practice. We will estimate crude and adjusted odds ratios (ORs), an approximation of the relative risk, and 95% CIs for ED in relation to use of 1 mg finasteride compared to unexposed, using conditional logistic regression with multivariable adjustment for identified covariates of importance. This study will provide information on the safety of finasteride 1mg prescribed to healthy young men for treatment of alopecia (also known as male patterned baldness).