Trenbolone acetate is a modified form of nandrolone.  The structure of trenbolone acetate is a 19-nor classification, which represents a structural change of the testosterone hormone. Trenbolone acetate lacks a carbon atom at the 19 position and carries a double bond at carbons 9 and 11. The position of these carbons slows its metabolism, which greatly increases its binding affinity to the AR, and inhibits it from undergoing aromatization into the corresponding estrogenic metabolite. Trenbolone acetate contains trenbolone modified with the addition of a carboxylic acid ester ( acetic acid ) at the 17β-hydroxyl group.  This facilitates the slow release of the AAS from the area of injection.