A comprehensive search of several computer-assisted databases was conducted (from each database's inception to August 2010, English language, any population). The databases included Ovid MEDLINE, Ovid Medline In-Process & Other Non-Indexed Citations, Ovid EMBASE, Ovid Cochrane Database of Systematic Reviews, Ovid Cochrane Central Register of Controlled Trials, and Scopus. Computer searches used combinations of medical subject headings or other key words (ie, impotence, erectile dysfunction, impotence, obesity, hyperlipidemia, dyslipidemia, hypertension, diabetes mellitus, smoking, metabolic syndrome, and insulin resistance). Limiting the searches to randomized controlled trials and similar studies produced a list of 1943 references. In addition, the reference lists of the retrieved articles were reviewed to identify eligible studies. The relevance of studies was assessed with a hierarchical approach on the basis of title, abstract, and the full manuscript.