When a man has an erection, his penis fills with blood. This blood is what gives the penis the rigidity it needs for sex. Many men with erectile dysfunction have problems with blood flow.
Pills for erectile dysfunction (ED) are classified as phosphodiesterase type 5 (PDE5) inhibitors and help increase blood flow to the penis. More specifically, these drugs increase the amount of nitric oxide in the body. The nitric oxide works with other substances to relax and open blood vessels so that blood can flow more freely, leading to a satisfactory erection.