Viagra (sildenafil) is a brand-name prescription drug that’s used to treat erectile dysfunction (ED). Learn about side effects, warnings, dosage, and more. NHS medicines information on dosage for sildenafil, how to take it and what to do if you miss a dose or take too much. 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. Medscape - Pulmonary hypertension, erectile dysfunction-specific dosing for Revatio, Viagra (sildenafil), frequency-based adverse effects, comprehensive interactions, contraindications, pregnancy. Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. 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, sold under the brand name Viagra among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. [4][8] It is also sometimes used off-label for the treatment of certain symptoms in secondary Raynaud's phenomenon. [9] Sildenafil oral tablet is a prescription medication used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). 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 (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors.