Testosterone butyrate, or testosterone butanoate, also known as androst-4-en-17ò-ol-3-one 17ò-butanoate, is a synthetic, steroidal androgen and an androgen ester â specifically, the C17ò butanoate ester of testosterone â which was first synthesized in the 1930s and was never marketed. Its ester side-chain length and duration of effect are intermediate between those of testosterone propionate and testosterone valerate.