Tadalafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). In combination with sexual stimulation, tadalafil works by increasing blood flow to the penis to help a man get and keep an erection. Tadalafil is also used to treat the symptoms of an enlarged prostate (benign prostatic hyperplasia-BPH). It helps to relieve symptoms of BPH such as difficulty in beginning the flow of urine, weak stream, and the need to urinate frequently or urgently (including during the middle of the night). Tadalafil is thought to work by relaxing the smooth muscle in the prostate and bladder.