Viagra (sildenafil) is a brand-name prescription drug that’s used to treat erectile dysfunction (ED). Learn about side effects, warnings, dosage, and more. 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. When a man is sexually stimulated, his body's normal response is to increase blood flow to his penis to produce an erection. Sildenafil (Viagra) is a tablet that's taken by mouth for erectile dysfunction (ED) in adults. It works as a phosphodiesterase-5 (PDE5) inhibitor to help people get an erection or keep an erection that lasts for sex. Below, we'll explain the origin story of Viagra, what this boner-benefitting pill can do, the benefits of Viagra for men, and the potential side effects of taking it. Pfizer to lose patent of drug Viagra, Indian companies gear up with copycat versions: Pfizer's patent for the formulation of Viagra, used to treat impotence in men, ends in the US in 2020. Learn more about Viagra, including its uses, dosage, side effects, and how to get it. Viagra Viagra (sildenafil) is used to treat erectile dysfunction or impotence in men. Includes Viagra side. Discover the mild and serious side effects of Viagra (sildenafil). Learn how to manage symptoms safely and when to seek medical help. Viagra relaxes muscles found in the walls of blood vessels and increases blood flow to particular areas of the body. Viagra is used to treat erectile dysfunction (impotence) in men. Find patient medical information for Sildenafil (Viagra, Revatio) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings.