Sildenafil, sold as Viagra and other trade names, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. Its effectiveness for treating sexual dysfunction in women has not been demonstrated.

Common side effects include headaches and heartburn, as well as flushed skin. Caution is advised in those who have cardiovascular disease. Rare but serious side effects include prolonged erections, which can lead to damage to the penis, and sudden-onset hearing loss. Sildenafil should not be taken by people who take nitrates such as nitroglycerin, as this may result in a severe and potentially fatal drop in blood pressure.