About Viagra
Viagra, generic name sildenafil citrate, is the famous little blue pill that's prescribed to treat erectile dysfunction, or impotence. There are a number of treatments and medications for erectile dysfunction, but Viagra is a popular choice for many men to help them achieve and retain an erection long enough to have a satisfying sexual experience.
Retention of Blood
To get an erection, a man needs blood to flow to the penis, fill it and stay there until he is able to climax, at which time the blood empties from the penis, and it becomes flaccid again. Men with erectile dysfunction aren't able to get blood to flow to the penis and stay there to create an erection.
Sexual arousal stimulates the brain to release chemicals that encourage the penis to relax, allowing blood flow. After climax, a different chemical called PDE5 is released to help the blood leave the penis and end the erection. Viagra inhibits the effects of PDE5, which allows the other chemicals that promote blood flow to the penis to continue being released. That way, blood remains in the penis and allows for a long-lasting erection.
Stimulation and Timing
Viagra doesn't allow for an erection without stimulation--men won't get a spontaneous erection without some sort of arousal. That allows for a natural erection when you want it, and not when you don't. The brain must release chemicals that allow for an erection for Viagra to work, and those are only released when a man is stimulated or aroused. It typically begins to take effect in about 15 to 30 minutes, and effects last around 4 hours. That doesn't mean that you can have a 4-hour erection; it just means that you'll have the ability to have an erection for a 4-hour period of time.
