The Nature of the Drug: Viagra (sildenafil citrate) was originally developed by Pfizer as a treatment for chest pain (angina) and pulmonary arterial hypertension. Clinical trials showed that the drug was not very effective for those problems; but Pfizer found that it did work for erectile dysfunction (ED). Viagra has been one of Pfizer’s most popular drugs, and is now the number-one ED treatment in the United States. Erectile dysfunction affects 40% of men over forty to some extent and 70% of men over seventy. Viagra is the most famous drug in the class called PED inhibitors, which act on an enzyme that dilates blood vessels and thereby enhance blood flow.
