To understand this, let’s look at how a normal male genital erection takes place. To put it simply, the erection is caused by the pressure of blood that flows into the penis when arousal occurs. It is the mechanism of this blood flow that is the important part when considering how Viagra works. One set of muscles has to relax to allow the blood to flow into the penis tissue, whilst another set of muscles constricts to stop this extra blood from escaping. So the blood is ‘trapped’ in the penis shaft tissue, which is what makes it hard and erect so that intercourse can take place. It is trapped in the tissue known as corpus cavernosum.
The corpus cavernosum takes an active part in this by releasing a chemical compound called nitric oxide from the cells of the corpus cavernosum tissue. This nitric oxide works as a messenger, which tells the muscle cells to relax and therefore let in the flow of blood to engorge the penis. To stop the reaction continuing too long after ejaculation, the nitric oxide is broken down by another compound, so the penis can return to its usual resting state.
Men who have impotence or erectile dysfunction are often not producing enough nitric oxide. The small amount they may produce is quickly broken down without it having chance to have the effect of relaxing the muscle to allow the blood flow into the penis. So what Viagra does is interfere in the cycle and prevents the nitric oxide being broken down, so that more of it can accumulate until there is enough to produce a satisfactory erectile function.
As Viagra does not make the body produce any extra amounts of any of its messenger compound, enzymes or hormones, it is not a true aphrodisiac, and this is why sexual stimulation is needed to achieve and maintain an erection. It works on the substances already present in the body, and it is because of this that it is so effective, and is successful in most men whatever the underlying cause for the erectile dysfunction may be.
Once the Viagra enters the body, its active ingredients have a life of around four hours, and then they are broken down and excreted by the digestive system. Viagra does not stay in the body and this, again, is one of the features that make it a safe and well-tolerated drug.