by Erich Rosenberger M.D.

Created on: September 19, 2007   Last Updated: September 20, 2007

Since it's release in 1998, Viagra has become a household word. It has not only created a revolution in the treatment of erectile dysfunction, but also become something of a cultural phenomenon. Viagra jokes are ubiquitous to the point of absurdity. But behind the advertisements by Bob Dole and the NASCAR sponsorships is a rather interesting medication. We all know what Viagra does, but how does it work? The answer to this is not as simple as it may seem.

In order to understand how Viagra works, you have to know a few basics of the nervous system, and the process by which an erection is created in a health man. There are two major parts of the human nervous system, the part you control directly and the part that keeps all the organs running smoothly in the background without you thinking about it. The automatic part is known as the "autonomic" nervous system, and learning the details of how it works is the bane of medical students worldwide.

The autonomic nervous system is then split in to two parts, known as the sympathetic and parasympathetic nervous system. These are the systems that are responsible for the "fight or flight" reflexes when you are in danger or under stress.

It is the parasympathetic response that is responsible for creating an erection. When a man gets an erection, the parasympathetic system triggers the release of Nitric Oxide. Nitric oxide stimulates the release of a chemical known as cyclic guanosine monophosphate (cGMP) which causes the smooth muscle in the corpus cavernosum of the penis to relax. This in turn leads to increased blood flow to the special tissues of the penis. It is this increase in blood flow that causes an erection. Following along so far?

As is obvious, an erection is not desirable to have all the time, and thus there needs to be a way to rid the tissues of the penis of the nitric oxide. This is done in a healthy man by an enzyme called phosphodiesterase type 5 (PDE-5). PDE-5 is released when the erection is no longer needed. It acts to break down the cGMP which is causing the erection. Once the cGMP is gone, the erection is gone as well.

Here's where Viagra steps in. Viagra blocks PDE-5 from breaking down the cGMP. If the cGMP remains present, the erection sticks around as well (no pun intended). In effect, Viagra turns off the "off switch". Note that because Viagra blocks the "off switch", it is still necessary to stimulate the man to get the erection in the first place. Viagra cannot create an erection, it only helps maintain one.

It should be noted that cGMP has many other functions in the body in addition to its role in creating erections. Preventing the degradation of cGMP by blocking PDE-5 can also lead to the side effects that can be reported with Viagra use, such as low blood pressure, headache, flushing, and palpitations.

The two other erectile dysfunction medications, Cialis and Levitra work in a very similar way to Viagra.

Because of these potential side effects, Viagra can only be prescribed by your doctor. If you have questions about Viagra or think it may be something that could help you, talk to your doctor.

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