Trenbolone is essentially a derivative of Nandrolone with some very significant differences in its chemical properties and strength. Trenbolone and its parent hormone Nandrolone both belong to a class/category of anabolic steroids known as 19-nor compounds, or 19-nors (short for 19-nortestosterone). 19-nor anabolic steroids are labeled as such because they lack the 19th carbon on their structure – this carbon exists on Testosterone and all other anabolic steroids with the exception of 19-nor compounds, such as Nandrolone and Trenbolone. This significantly changes around the properties of an anabolic steroid and makes it a Progestin, which will be discussed further shortly. In Trenbolone, this missing carbon atom at the 19thposition (which is in reality a whole methyl group) is replaced by double-bonds between the two carbon atoms that the 19th carbon was originally bound with (this differs from Nandrolone where the lacking 19th carbon is simply replaced with a hydrogen atom instead of double-bonds in Trenbolone’s case). This lack of a 19th carbon is what makes 19-nor compounds very resistant to the aromatase enzyme and therefore very resistant to any estrogen conversion – however, this is not the whole story for Trenbolone when it comes to aromatization.