Altrenogest, also known as 17α-allyl-19-nor-δ 9,11 -testosterone or as 17α-allylestra-4,9,11-trien-17β-ol-3-one, is a synthetic estrane steroid and derivative of 19-nortestosterone and 17α-allyltestosterone , or of 17α-allyl-19-nortestosterone .    It is one of only two marketed progestins that possesses a 17α-allyl group, the other being allylestrenol .   Most other progestins possess a 17α- ethynyl group , while AAS, if they are 17α-substituted, are usually 17α-alkylated (with a methyl or ethyl group ).   Altrenogest is the 17α-allylated derivative of the AAS trenbolone (and hence can also be referred to as allyltrenbolone or allyltrienolone), which itself is the 9,11-didehydro analogue of the AAS nandrolone (19-nortestosterone).   Altrenogest is also closely related to norgestrienone .