Quinestrol is a synthetic estrogen that is effective in hormone replacement therapy.^1,2 It is a 3-cyclopentyl ether of ethynyl estradiol. After gastrointestinal absorption, it is stored in adipose tissue, where it is slowly released and metabolized in the liver to its active form, ethinyl estradiol. Quinestrol has found limited use in suppressing lactation in postpartum women and, in combination with synthetic progestogens, as contraceptive therapy, although additional studies are needed for both applications.