Melengestrol (INN, BAN) is a steroidal progestin of the 17α-hydroxyprogesterone group and an antineoplastic drug which was never marketed. An acylated derivative, melengestrol acetate, is used as a growth promoter in animals. While melengestrol is sometimes used as a synonym for melengestrol acetate, what is usually being referred to is melengestrol acetate and not melengestrol.