How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. Do not take more or less of it or take it more often than prescribed by your doctor. Some people may also have ringing in their ears tinnitus or dizziness. Sildenafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. Severe liver disease. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. Stop taking VIAGRA and call your healthcare provider right away if you have any sudden vision loss sudden hearing decrease or hearing loss. · Follow all directions on your prescription label and read all medication guides or instruction sheets. Revatio is usually taken three times each day, about 4 to 6 hours . VIAGRA (sildenafil citrate) is prescription medicine used to treat erectile dysfunction (ED). VIAGRA is not for women or children. Please see Full Prescribing Information and . 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 .