How Does Viagra Work?

The three stages of male sexual function can be defined as (1) arousal; (2) erection; and (3) ejaculation. Viagra assists men who are having trouble turning their arousal into an erection, making it nearly impossible to ejaculate.

Viagra is not an aphrodisiac; that is, it will not create arousal in a man who is not aroused. However, Viagra will allow many men with erectile dysfunction to achieve an erection when they are aroused by sexual stimulation, such as kisses or touching. Unlike muscles, which move by contraction, the penis achieves an erection by filling up with blood and then keeping the blood in the penis. When a man becomes sexually aroused, his brain transmits a signal to nerve cells in the penis, which begin to produce nitric oxide. Nitric oxide, in turn, produces cGMP, which causes the arteries in the penis to dilate, and blood to flow in. This increase in blood flow leads to an erection, as the penis becomes stiff. Veins in the penis then restrict, keeping blood flow from leaving the penis and preserving the erection.

Viagra works by increasing blood flow to the penis, making it easier for a man to become erect and maintain an erection when sexually aroused. The specific way that Viagra does this is rather ingenuous. Viagra’s active ingredient, sildenafil citrate, disables an enzyme called PDE5 which decomposes cGMP, the agent that causes dilation of the arteries in the penis. A greater amount of cGMP in the penis leads to greater blood flow and an increased erection. Erectile dysfunction often occurs when the blood vessels in the penis do not open up in response to the brain’s signal of arousal; thus, Viagra works to correct this problem.

Viagra takes about half an hour to take effect and may last for as long as four hours. However, Viagra should not cause a man to remain erect for hours. Rather, a man’s erection will diminish after sex just as it usually does. In fact, staying erect for more than four hours after sex is a potentially dangerous side effect about which a man should consult his physician.

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