How Viagra Works:
"The Nitric Oxide Story"

Adapted from original story in New York Times (March 28, 1998)

Photo courtesy of the L.A. Times
When a man is sexually stimulated, his brain sends signals to the nerves surrounding the penis. Those nerve cells release nitric oxide (NO), which in turn causes the penis to make another chemical, cyclic guanosine monophosphate (cGMP). cGMP is the key to having an erection. It widens blood vessels in the penis, and so blood gushes in, causing the penis to become rigid.

As long as the man remains sexually stimulated, he continues to produce cGMP. But at the same time, he makes another chemical, phosphodiesterase Type 5 (PDE-5), which destroys cGMP. The result is an equilibrium: the production and degradation of cGMP are in balance, and the penis remains erect. When cGMP stops being produced, PDE-5 takes over, destroying the leftover chemical. The erection disapears.

Viagra blocks PDE-5. If a man who is impotent takes the drug, it boosts the effects of cGMP in his penis by slowing its degradation. The result can be an erection in a man who would not normallly be able to have one.

PDE-5 is not found in important quantities elsewhere in the body--the coronary arteries, for example. That is why Viagra did not alleviate angina.


this is a navigational image map, please load this image to continue.