Etynodiol (INN), or ethynodiol (BAN), also known as 3β-hydroxynorethisterone, is a steroidal progestin related to norethisterone which was never marketed. A diacylated derivative, etynodiol diacetate, is used as a hormonal contraceptive. While etynodiol is sometimes used as a synonym for etynodiol diacetate, it usually refers to etynodiol diacetate, not etynodiol.
Etynodiol is a prodrug of norethisterone, and is converted immediately and completely into norethisterone. In addition, etynodiol is an intermediate in the conversion of the prodrug lynestrenol into norethisterone.
Etynodiol is a 19-nortestosterone derivative. Structurally, it is almost identical to norethisterone and lynestrenol, differing only in its C3 substituent. Whereas norethisterone has a ketone at C3 and lynestrenol has no substituent at C3, etynodiol has a hydroxyl group at the position.