Mestranol's the 3-methyl ether of ethinylestradiol. It was the estrogen used in many of the first oral contraceptives. It's a biologically inactive prodrug of ethinylestradiol to which it's demethylated in the liver with a conversion efficiency of 70% (50 µg of mestranol's pharmacokinetically bioequivalent to 35 µg of ethinylestradiol).… (More on Mestranol)