You can take sildenafil with or without food. You may opt-out of email communications at any time by clicking on the unsubscribe link in the e-mail. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. The following nonprescription or herbal products may interact with sildenafil: cimetidine Tagamet HB , St. Some medications should not be taken with sildenafil. Take sildenafil exactly as directed.By Ginger Skinner Last updated: June 14, If you’re looking for a less costly Viagra, you might want to ask your doctor about sildenafil. It’s the active . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual . Sildenafil oral tablet is available as a brand-name drug and as a generic drug. Brand names: Viagra, Revatio. Sildenafil comes in three forms: an oral tablet, an .