Pentagestrone (INNTooltip International Nonproprietary Name), also known as 17α-hydroxyprogesterone 3-cyclopentyl enol ether, is a steroidalprogestin of the 17α-hydroxyprogesterone group that was never marketed.[1][2] An acetateester, pentagestrone acetate (Gestovis, Gestovister), has been marketed for clinical use.[1] Pentagestrone was described in the literature in 1960.[1]