Methenolone is a derivative of dihydrotestosterone. It contains one additional double bond between carbons 1 and 2, which helps to stabilize the 3-keto group and increase the steroid’s anabolic properties, and an additional 1-methyl group, which gives the steroid some protection against hepatic metabolism. Primobolan Depot makes use of methenolone with a carboxylic acid ester (enanthoic acid) attached to the 17-beta hydroxyl group. Esterified steroids are less polar than free steroid, and are absorbed more slowly from the area of injection. Once in the bloodstream, the ester is removed to yield free (active) methenolone. Esterified steroids are designed to prolong the window of therapeutic effect following administration, allowing for a less frequent injection schedule compared to injections of free (unesterified) steroid.