If we combine this information with your protected health information, we will treat all of that information as protected health information and will only use or disclose that information as set forth in our notice of privacy practices. Its effects often last for 4 to 5 hours. Continue to take sildenafil even if you feel well. Some medications should not be taken with sildenafil. The following nonprescription or herbal products may interact with sildenafil: cimetidine Tagamet HB , St.Viagra – Uses, Side Effects, and More Generic Name (S): sildenafil Uses Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects .