Levonorgestrel is a contraceptive drug, known most commonly as the morning after pill. It is composed of a synthetic form of the hormone progesterone, a type of progestin. Levonorgestrel works by binding to the progesterone and estrogen receptors. It has only been evaluated for its use in one research study involving Japanese quail. In humans, Levonorgestrel is used to prevent pregnancy and in the prevention of ovarian and endometrial cancer.