Tadalafil, sold under the brand name Cialis among others, is a medication used to treat erectile dysfunction (ED), benign prostatic hyperplasia (BPH), and pulmonary arterial hypertension. It is a tablet taken by mouth. Onset is typically within half an hour and the duration is up to 36 hours.

Common side effects include headache, muscle pain, flushed skin, and nausea. Caution is advised in those with cardiovascular disease. Rare but serious side effects include a prolonged erection that can lead to damage to the penis, vision problems, and hearing loss. Tadalafil is not recommended in people taking nitrovasodilators such as nitroglycerin, as this may result in a serious drop in blood pressure. Tadalafil is a PDE5 inhibitor which increases blood flow to the penis. It also dilates blood vessels in the lungs, which lowers the pulmonary artery pressure.

Tadalafil was approved for medical use in the United States in 2003. It is available as a generic medication in the United States and United Kingdom. In 2017, it was the 282nd most commonly prescribed medication in the United States, with more than one million prescriptions.