Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Do not take more or less of it or take it more often than prescribed by your doctor. Do not mix the liquid with other medications or add anything to flavor the medication. What special dietary instructions should I follow? If you are taking sildenafil to treat erectile dysfunction, follow your doctor’s directions and the guidelines in this paragraph. Shake the liquid well for 10 seconds before each use to mix the medication evenly. Severe liver disease. · Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men. Another brand of sildenafil is Revatio, which is used to treat . Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes .