Alprostadil is the active ingredient that is used in Vitaros. It is a medication that is used to treat erectile dysfunction that belongs to a class of medications known as prostaglandins - specifically prostaglandin E1 (PGE1). Prostaglandins are naturally occurring compounds that play many roles in the human body including in inflammation and blood flow in a blood vessel. Alprostadil functions as a vasodilator, expanding blood vessels to facilitate improved blood flow to the penis, to help men get an erection.