Do not start these medications while taking sildenafil without discussing it with your healthcare provider. The combination can cause a dangerous fall in your blood pressure. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Take sildenafil as needed before sexual activity. An inherited eye disease that affects the retina. These medicines all work well for ED.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 . It’s a prescription drug that’s used in adult males* with ED. With ED, you have trouble getting or keeping an erection. Viagra treats ED by increasing the amount .  · 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 .