Sildenafil is available as a generic drug in the United States, labeled for pulmonary arterial hypertension, [98] and to treat erectile dysfunction, as the patent expired in April 2020. Sildenafil works by blocking an enzyme in the body called PDE5, which helps relax certain blood vessels. For erectile dysfunction, it increases blood flow to the penis when aroused. Sildenafil is used to treat erectile dysfunction in adult men or pulmonary arterial hypertension in adults and children, depending on the brand or formulation. Includes sildenafil side effects, interactions, and indications. Learn about sildenafil (Viagra) usage and dosing. Read the latest news and reviews about the drug as well as potential side effects and popular alternatives. In the U.S., you can legally buy generic Viagra (sildenafil) online, but only with a prescription from a licensed healthcare professional. Sildenafil for erectile dysfunction is not an over‑the‑counter (OTC) medicine in the U.S., so you cannot legally buy it without a prescription. Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). Learn about side effects, drug interactions, dosages, warnings, and more. Sildenafil oral tablet is available as the brand-name drugs Viagra and Revatio. It’s also available as a generic drug. Generic drugs usually cost less than the brand-name version. Sildenafil is used to treat erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. Sildenafil: Brand-name Viagra typically sells for $50 or more per dose. Generic sildenafil can sell for as low as $12 per dose. Tadalafil: Brand-name Cialis may cost up to $70 for a 20-mg. Available in all 50 states, Marley Drug is an online pharmacy providing low-cost medications, great customer service, and free home delivery.