Tadalafil - commonly sold under the brand name Cialis - is a prescription medication that is used to treat erectile dysfunction (ED) and the symptoms of benign prostatic hyperplasia (BPH). Tadalafil may also be prescribed as a treatment for pulmonary arterial hypertension (PAH; high blood pressure in the blood vessels that carry blood to the lungs). Tadalafil is classified as a phosphodiesterase (PDE) inhibitor, a group of medications that relaxes muscles and increases blood flow to certain areas of the body.
Because tadalafil encourages circulation throughout the body, it can help increase blood flow to the penis during sexual stimulation. It should be noted that tadalafil does not protect against sexually transmitted diseases.