An androgen or anabolic steroid ester is an ester of an androgen/anabolic steroid (AAS) such as the natural testosterone or dihydrotestosterone (DHT) or the synthetic nandrolone (19-nortestosterone). Esterification renders AAS into metabolism-resistant prohormones of themselves, improving oral bioavailability, increasing lipophilicity, and extending the terminal half-life (which necessitates less frequent administration). In addition, with intramuscular injection, AAS esters are absorbed more slowly into the body, further improving the terminal half-life. Aside from differences in pharmacokinetics (e.g., duration), these esters essentially have the same effects as the parent drugs. They are used in androgen replacement therapy (ART), among other indications. Examples of androgen esters include the testosterone esters testosterone cypionate, testosterone enanthate, testosterone propionate, and testosterone undecanoate and the nandrolone esters nandrolone decanoate and nandrolone phenylpropionate.