Clostebol propionate (brand name Yonchlon), also known as 4-chlorotestosterone 17ò-propionate or as 4-chloroandrost-4-en-17ò-ol-3-one 17ò-propionate, is a synthetic, injected anabolic-androgenic steroid (AAS) and a derivative of testosterone. It is an androgen ester â specifically, the C17ò propionate ester of clostebol (4-chlorotestosterone) â and acts as a prodrug of clostebol in the body. Clostebol acetate is administered via intramuscular injection.