Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Common ones include: Flushing of the skin. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox. If your dose is different, do not change it unless your doctor tells you to do so. You may take this medicine with or without food.Sildenafil oral tablet is available as the brand-name drugs Viagra and Revatio. It’s also available as a generic drug. Generic drugs usually cost less than the brand-name . Drug Images What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. . For treatment of erectile dysfunction: For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual .