Dydrogesterone (INN, USAN, BAN) (brand name Duphaston), also known as isopregnenone or 6-dehydroretroprogesterone, as well as 9β,10α-pregna-4,6-diene-3,20-dione, is a steroidal progestin of the retroprogesterone group that was developed in the 1950s and introduced for clinical use in 1961. It is available widely throughout Europe, including the United Kingdom and many other European countries, and is also marketed in Australia, Hong Kong, and India. The drug was previously marketed in the United States as well, but is now no longer available in this country.