The acetate salt of megestrol, a synthetic derivative of the naturally occurring female sex hormone progesterone, with progestogenic, antiestrogenic, and antineoplastic activities. Mimicking the action of progesterone, megestrol binds to and activates nuclear progesterone receptors (PRs) in the reproductive system and pituitary; ligand-receptor complexes are translocated to the nucleus where they bind to progesterone response elements (PREs) located on target genes. Megestrol