What special precautions should I follow? Children 1 year of age and older weighing 20 kg or less—10 mg 3 times a day. If your dose is different, do not change it unless your doctor tells you to do so. However, the dose is usually not more than 80 mg 3 times a day. If you are taking sildenafil to treat erectile dysfunction, you should know that it does not cure erectile dysfunction or increase sexual desire. These are commonly prescribed for an enlarged prostate or male pattern baldness.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 adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the .  · 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. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed. How does Viagra work? To understand what Viagra does and how it works, you must first have an understanding of the way in which a man gains an erection. When the brain becomes aroused, it sends signals to the penis which leads to the release of a chemical called cGMP. This chemical relaxes certain muscle cells in the erectile tissue of the.