The levorotatory form of norgestrel and synthetic progestogen with progestational and androgenic activity. Levonorgestrel binds to the progesterone receptor in the nucleus of target cells, thereby stimulating the resulting hormone-receptor complex, initiating transcription, and increasing the synthesis of certain proteins. This results in a suppression of luteinizing hormone (LH) activity and an inhibition of ovulation, as well as an alteration in the cervical mucus and endometrium. or A form of the hormone progesterone that is made in the laboratory and used to prevent pregnancy. It is being studied in the prevention of ovarian and endometrial cancer, and in the treatment of other conditions. Levonorgestrel is a type of oral contraceptive. Also called L-norgestrel and Plan B.