If too much is used, the chance of side effects is increased. 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. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. However the dose is usually not more than 40 mg 3 times a day. Slowly pull back the plunger until the required dose. Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men.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 . Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. . What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. .