Do not take a double dose to make up for a missed one. Severe liver disease. Continue to take sildenafil even if you feel well. An inherited eye disease that affects the retina. Brand names Why is this medication prescribed? · For example, a year-old might start at a dose of 50 milligrams (mg), while a year-old might have a starting dose of 25 mg. This is because, in older people, the body clears Viagra from your. 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 . The normal dose when starting Viagra is 50 mg, as needed. The maximum dose of Viagra is mg each day. Doses above the maximum dose, such as mg per day, will increase the risk of side effects.