Viagra (generic name sildenafil) is a medication used to treat men who have trouble getting an erection, a condition called erectile dysfunction or impotence. The U.S. Food and Drug Administration approved Viagra for erectile dysfunction, but not to prolong erections. Viagra will not help delay ejaculation. Viagra works by increasing blood flow to the penis. With sexual stimulation, this causes an erection. You won't get an erection by simply taking a Viagra pill. Viagra improves the ability to have erections in about 80 percent of the men who take it. Viagra is available in doses of 25 to 100 mg. For best results, take it one hour before having sex. The drug can be effective anywhere from ten minutes to four hours after taking a dose. It works faster when you take it on an empty stomach. When the sexual experience is over, the erection goes away: Viagra doesn't help you keep an erection. Don't take more than one dose of Viagra per day because this greatly increases the risks of severely low blood pressure. Sources:Micromedex® Healthcare Series. Thomson Micromedex, 2006.Viagra product information, Pfizer Labs, 2006. Medina P. “Effects of sildenafil on human penile blood vessels. buy viagra online now!