Medroxyprogesterone, chlormadinone, megestrol and melengestrol are synthetic analogues of progesterone that are commonly administered orally as acetate derivatives. They are used for synchronisation of oestrous, but have also been used as growth promoters in cattle. (21-23) Synthetic gestagen residue levels are highest and most persistent in fat. The unchanged parent molecules are used for monitoring purposes. (21-23)