Testosterone undecanoate (Test U,TU), or testosterone 17β-undecanoate, is a synthetic androstane steroid and a derivative of testosterone. It is an androgen ester; specifically, it is the C17β undecylate (undecanoate) ester of testosterone. A related testosterone ester with a similarly very long duration is testosterone buciclate.
Testosterone undecanoate or testosterone undecylate is an ester of testosterone. This hormone is used in androgen replacement therapy primarily for the treatment of male hypogonadism, and is currently under research for use as a male contraceptive. It is sold and distributed under the brand names Andriol, Undestor, Nebido, Pantestone, Restandol, Cernos Depot, Nebido-R and Reandron 1000.