Ethinylestradiol is a synthetic estrogen with high oral hormonal potency. (19) It is rapidly reabsorbed from the gastrointestinal tract and the presence of an ethinyl at the 17-position reduces hepatic first-passage metabolism. (19) It is excreted in urine and some is found in faeces. Ethinylestradiol is illegally used in animal husbandry as an anabolic (19) and is excreted as the parent molecule in faeces, and as glucuronide or sulphate tracer in urine. (20)