Sorry something went wrong with your subscription Please, try again in a couple of minutes Retry. Continue to take sildenafil even if you feel well. Do not take a double dose to make up for a missed one. This increased blood flow can cause an erection. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. Do not take more or less of it or take it more often than prescribed by your doctor. Food and Drug Administration has approved fifteen drug manufacturers to market generic sildenafil in the United States.Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult . Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes .