Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Also tell your doctor if you have or have ever had pulmonary veno-occlusive disease PVOD; blockage of veins in the lungs ; a stomach ulcer; heart, kidney, or liver disease; a heart attack; heart failure; angina chest pain ; an irregular heartbeat; a stroke; chest pain; high or low blood pressure; high cholesterol; a bleeding disorder; blood circulation problems; blood cell problems such as sickle cell anemia a disease of the red blood cells , multiple myeloma cancer of the plasma cells , or leukemia cancer of the white blood cells ; conditions affecting the shape of the penis e. Proper Use Use sildenafil exactly as directed by your doctor. They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. If your dose is different, do not change it unless your doctor tells you to do so. Patients should always ask their doctors for medical advice about adverse events.Learn about uses, how it works, and more for Viagra (sildenafil). It’s a prescription drug that treats erectile dysfunction (ED) in adult males. Health . Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in . VIAGRA contains sildenafil, which is the same medicine found in another drug called REVATIO. REVATIO is used to treat a rare disease called pulmonary arterial .