Viagra (generic name sildenafil) is a widely-used medication for treating erectile dysfunction (ED). You probably don’t have a clue how many men use this blue pill. According to a study by E. Selvin et al. (Johns Hopkins Bloomberg School of Public Health, 2007), prevalence of the disease was 18.4% in males aged >/=20, so the scientists suggested that ED affected more than 18 million men in the United States. As of today, these figures may be even higher.