Estrogen ester

An estrogen ester is an ester of an endogenous, steroidal estrogen, generally estradiol but also estrone or estriol. Esterification renders these drugs into metabolically-resistant prohormones of their respective parent estrogen, improving oral bioavailability, increasing lipophilicity, and extending half-life (which necessitates less frequent administration). In addition, with intramuscular injection, they are absorbed more slowly into the body, further improving half-life.