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. 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. To buy Viagra online or in person, you need a prescription. Telehealth brands can help you get quickly and discreetly. “Generic Viagra” is often just the main ingredient, sildenafil. One main. Discover the mild and serious side effects of Viagra (sildenafil). Learn how to manage symptoms safely and when to seek medical help. Viagra (sildenafil) is a prescription medication that treats erectile dysfunction (ED). Viagra is an oral medication. It’s available as 25 mg, 50 mg, and 100 mg tablets. You can take a dose about 1 hour before sexual activity. Viagra is available as a lower-cost generic. 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. 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 Patient Information. Viagra is used to treat problems relating to male sexual function, particularly problems concerning the ability to achieve and maintain an erection. Learn how to take Viagra safely to treat erectile dysfunction. Swallow a 50 mg dose of Viagra 30-60 minutes before sex.