(Sildenafil Citrate) magnifies the activity of a chemical in the penis called nitric oxide, which is in charge of erections. This action should coincide with sexual activity (foreplay is needed). The maximum blood level occur in 60 minutes.
Sexual activity can continue from 30 minutes till six hours after taking the pill. A high-fat meal will decrease the amount of medication absorbed into the blood leading to violation to effectivness.
Viagra works better if taken one hour before or two and a half hours after eating.
In March 1998, the FDA approved Viagra (Sildenafil Citrate) for clinical use after several years of supervised drug testing on 1,500 men.
Further trials bring the total research experience to over 3,000 men.
During first six months after the drug's release, the Center for Sexual Function at Lahey Hospital & Medical Center evaluated 714 men that took Viagra.