All drugs have the potential to cause side effects and Viagra is no different. In general PDE-5 inhibitors such as Viagra are well tolerated. Years of clinical studies and trials have revealed Viagra to be a safe drug which is only likely to provoke mild to moderate side effects in a small proportion of its users. Less than one percent of Viagra users experience serious side effects when taking the medication. The chambers also contain a network of blood vessels. When those blood vessels relax and widen, blood rushes in. The resulting pressure is what causes an erection. PDE-5 can …