Estradiol cyclooctyl acetate (E<sub>2</sub>COA), or estradiol 17ò-cyclooctylacetate, also known as estra-1,3,5(10)-triene-3,17ò-diol 17ò-cyclooctylacetate, is an estrogen medication and an estrogen ester â specifically, the 17ò-cyclooctylacetate ester of estradiol â which has been studied for use in hormone replacement therapy for ovariectomized women and as a hormonal contraceptive in combination with a progestin but was never marketed. It has greater oral bioavailability than does micronized estradiol due to absorption via the lymphatic system and hence partial bypassing of first-pass metabolism. It is approximately twice as potent as micronized estradiol orally and has a comparatively reduced impact on liver parameters such as changes in sex hormone-binding globulin production. It was investigated in combination with desogestrel as a birth control pill, but resulted in unacceptable menstrual bleeding patterns and was not further developed.