This condition may require prompt medical treatment to prevent serious and permanent damage to your penis. Ask your doctor if you have any questions. It continues to work for up to 4 hours, although its action is usually less after 2 hours. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox. It was initially studied for use in hypertension high blood pressure and angina pectoris a symptom of ischaemic heart disease.VIAGRA is available by prescription only in 25 mg, 50 mg, and mg tablets. Patients should always ask their doctors for medical advice about adverse events. You are encouraged to report adverse events related to Viatris products by calling (U.S. only). If you prefer, you may contact the U.S. Food and Drug Administration (FDA. mg Typical dosages The following information describes commonly recommended dosages for ED. However, be sure to take the dosage your doctor prescribes for you. . Brand names: Revatio, Viagra Drug classes: Agents for pulmonary hypertension, Impotence agents. Medically reviewed by Kaci Durbin, MD. Last updated on .