Nandrolone and Tren belong to a special unique category of anabolic steroids known as Progestins. Nandrolone itself is quite structurally similar to Testosterone. However, Nandrolone differs from Testosterone due to the lack of the 19th carbon. This is why Nandrolone and Trenbolone are often referred to as 19-nortestosterone compounds, meaning a carbon atom is missing at the 19th position. As such, any compound relating to (or is a derivative of) Nandrolone is also commonly referred to as a ’19-nor’ compound, including Nandrolone itself.
Trenbolone being a Nandrolone derivative is of course missing the aforementioned carbon atom at the 19th position (which is in reality a whole methyl group) and this carbon atom is instead 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 increases the resistance of 19-nor compounds to interaction with 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. Trenbolone also contains modifications at carbons 19 and 11, where one hydrogen atom was removed from each carbon so that carbons 19 and 11 become double-bonded with their neighboring carbon atoms in their respective cycloalkane rings. These additional modifications of double-bonds at carbon 19 and 11 are what provides Trenbolone not just increased resistance to aromatization, but to become completely immune to it and be unable to interact what so ever with the aromatase enzyme. These different modifications are also responsible for granting Trenbolone with the extreme anabolic and androgenic strength ratings it is so well known for.
19-nor Progestational compounds such as Nandrolone and Trenbolone exhibit various effects and side effects in the body that are unique only to 19-nor compounds, and are not seen among any other types of steroids. Studies have demonstrated that 19-nor anabolic steroids tend to exhibit binding affinity for the Progesterone receptors in the body. Trenbolone in particular possesses very strong binding affinity (much stronger than Nandrolone) for the Progesterone receptor 1. As mentioned above, this is one of the factors involved where Trenbolone possesses side effects that are almost never seen in other anabolic steroids that are not Progestins. Progestogenic side effects are almost identical to Estrogenic side effects, and they include: severe endogenous Testosterone production shutdown/suppression, gynecomastia, and water retention. It has been determined that the activity of Progestins is closely correlated with the activity of Estrogen in the body. This is why care must be taken to understand the Progestogenic properties of Nandrolone and its derivatives before using them, as well as how to properly deal with the associated Progestogenic effects.
19-nor compounds (Nandrolone derivatives) are preferred by athletes and bodybuilders for many of the same reasons that they would prefer DHT derivatives. 19-nor compounds are either highly resistant to aromatization, or do not aromatize into Estrogen at all (in Trenbolone’s case), and therefore eliminate the potential for Estrogen-related side effects such as water retention/bloating and gynecomastia. These types of steroids also do not interact with the 5AR enzyme, or they interact with it in very miniscule amounts (in Nandrolone’s case). However, Progestogenic effects are a concern that must be fully understood. For a further in-depth description of what these Progestin effects are, please refer to the specific profiles for both Nandrolone as well as Trenbolone where this is delved into greater detail.