Trengestone ( INN) (brand names Reteroid, Retroid, Retrone), also known as 1,6-bis-dehydro-6-chloro-retroprogesterone or as 6-chloropregna-1,4,6-triene-3,20-dione, is a steroidalprogestin that was introduced by Roche in 1974 and was formerly used to treat menstrual problems.