This boosts blood flow and helps you get an erection from sexual activity. Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take. From Mayo Clinic to your inbox Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health. Its effects often last for 4 to 5 hours. 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 intercourse. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide.The Savings Offer and Program expire on 12/31/ For further information, call , visit test1.ru, or write: Viatris Inc., P.O. Box , Mission, KS . Viagra dosage is not based on weight, but your age can affect your dosage. Specifically, you may have a lower starting dosage than usual if you’re over age Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but .