It takes from 30 minutes to 1 hour for Viagra (sildenafil) to start working, and the effects will last for about 4 hours. It is used to treat erectile dysfunction.

Hardness and duration of erections increase with increased dose. Viagra is given as an oral pill, so it has to be absorbed from your stomach to get into your blood and reach your penis. Studies show that Viagra is rapidly absorbed. It reaches its highest blood level between 30 and 120 minutes after taking it. After 4 hours, half of the Viagra has been broken down by the liver. It continues to decrease over the next 20 hours.

Viagra may take longer to work if you take it after a fatty meal because fat slows down absorption in your stomach. Men over age 65 and men with liver disease or severe kidney disease may have longer effects from Viagra, and the dose may need to be lower.

Viagra works by increasing smooth muscle relaxation in the part of the penis called the corpus cavernosum. When the penis is stimulated, a substance called nitric oxide is released. In a series of steps, nitric oxide is turned into a substance called cGMP. This substance causes smooth muscle relaxation that allows more blood to flow into your penis. Viagra inhibits the breakdown of cGMP, which makes an erection harder and longer lasting. Since this process only starts with stimulation of the penis and the release of nitric oxide, Viagra will not give you an erection without your penis also being stimulated.

Viagra can make your penis stay erect longer, but it may not make you last longer. The time to orgasm and ejaculation may not change. Men with early ejaculation or premature ejaculation may not be helped by Viagra. The American Urological Association does not recommend Viagra as a treatment for premature ejaculation.

Erectile dysfunction has many causes. Viagra is not a cure. It does not increase your desire for sex. The most common cause of erectile dysfunction is decreased blood supply to the penis, which may be a warning of decreased blood supply to other parts of your body. Your doctor may check you for high blood pressure, heart disease and type 2 diabetes.

Erectile dysfunction can also be caused by depression, anxiety and drug or alcohol abuse. Your doctor may help you manage these problems before or in addition to prescribing Viagra.