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.This drug does not protect against?sexually transmitted diseases?(such as?HIV,?hepatitis B,?gonorrhea,?syphilis).