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. Do not use more of it and do not use it more often than your doctor ordered. Ask your doctor if you have any questions. Children—Use is not recommended. Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day. · Viagra is usually taken only when needed, 30 minutes to 1 hour before sexual activity. You may take it up to 4 hours before sexual activity. Do not take two doses at . Viagra works at its best within a few hours after it’s taken. In most people, the drug is most effective about 1 hour after it’s taken. Over time, Viagra is slowly .  · Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be .