Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection. Keep out of the reach of children. Sildenafil may cause side effects. Other uses for this medicine This medication is sometimes prescribed for other uses; ask your doctor or pharmacist for more information. Sildenafil is also used in both men and women to treat the symptoms of pulmonary arterial hypertension.Learn about uses, how it works, and more for Viagra (sildenafil). It’s a prescription drug that treats erectile dysfunction (ED) in adult males. What is sildenafil? Sildenafil is a prescription drug. It comes in the form of a tablet and suspension (liquid). Both are taken by mouth. It also comes in an intravenous (IV) form, . Viagra; Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called .