Cialis and Viagra are used to treat erectile dysfunction, more commonly known as impotence.

A man is impotent if he cannot achieve or sustain an erect penis for sexual activity.

Cialis and Viagra are oral treatments for erectile dysfunction.

Unlike previously approved treatments for impotence, Viagra and Cialis do not directly cause penis erection, but affect the response to sexual stimulation. The drugs act by enhancing the smooth muscle relaxation using nitric oxide, a chemical that is normally released in response to sexual stimulation.

This smooth muscle relaxation allows increased blood flow into certain areas of the penis leading to an erection.