The majority of the information identified addressed the question about comparative clinical effectiveness of the PDE=5 inhibitors for the treatment of erectile dysfunction. Two meta-analyses demonstrated no significant differences in efficacy of the three PDE-5 inhibitors in the treatment of erectile dysfunction, while another demonstrated that sildenafil might be more efficacious than vardenafil. All three meta-analyses were based upon the statistical method of indirect comparison, not direct head-to-head comparisons. Further, the meta-analysis that found sildenafil to be superior to vardenafil had relatively restrictive inclusion criteria and only looked at maximal fixed dosages of each drug. Two additional RCTs also had conflicting results, one favouring vardenafil over sildenafil and the other demonstrating no difference. The clinical importance of differences in efficacy measures was not stated in the RCT or meta-analysis that demonstrated differences between PDE-5 inhibitors. One observational study suggested that adverse effects might be prolonged with tadalafil, but this did not appear more bothersome to the patients. Overall, the included reports suggest that there are minimal differences between PDE-5 inhibitors in the treatment of erectile dysfunction in men over the age of 18 years.