Sildenafil

Sildenafil, sold under the brand name Viagra among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension.^[5][9] It is also sometimes used off-label for the treatment of certain symptoms in secondary Raynaud's phenomenon.^[10] It is unclear if it is effective for treating sexual dysfunction in females.^[9] It can be taken orally (swallowed by mouth), intravenously (injection into a vein), or through the sublingual route (dissolved under the tongue).^[9][11] Onset when taken orally is typically within twenty minutes and lasts for about two hours.^[9]

Common side effects include headaches, heartburn, and flushed skin.^[9] Caution is advised in those with cardiovascular disease.^[9] Rare but serious side effects include vision problems, hearing loss, and prolonged erection (priapism) that can lead to damage to the penis.^[9] Sildenafil should not be taken by people on nitric oxide donors such as nitroglycerin, as this may result in a serious drop in blood pressure.^[9]

Sildenafil acts by blocking phosphodiesterase 5 (PDE5), an enzyme that promotes breakdown of cGMP, which regulates blood flow in the penis.^[9] It requires sexual arousal to work, and does not by itself cause or increase sexual arousal.^[9] It also results in dilation of the blood vessels in the lungs.^[9]

Pfizer originally discovered the medication in 1989 while looking for a treatment for angina.^[12] It was approved for medical use in the United States and in the European Union in 1998.^{[6][9][12][13]} In 2022, it was the 157th most commonly prescribed medication in the United States, with more than 3 million prescriptions.^[14][15] It is available as a generic medication.^[16][17] In the United Kingdom, it is available over-the-counter (OTC).^[18]