Testosterone propionate is a modified form of testosterone, where a carboxylic acid ester (propionic acid) has been attached to the 17-beta hydroxyl group. Esterified forms of testosterone are less polar than free testosterone, and are absorbed more slowly from the area of injection. Once in the bloodstream, the ester is removed to yield free (active) testosterone. Esterified forms of testosterone 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. The half-life of testosterone propionate is approximately 2 days after injection. The propionate ester slows the rate in which the testosterone is released from the injection site, but only for a few day. Therefore, it’s much faster acting than other esters and requires a more frequent injection schedule. For those who aren’t bothered by that testosterone propionate is usually incorporated into bulking phases of training, when added water retention will be of little consequence, users are generally more concerned with raw mass then definition. Some do incorporate it into cutting cycles as well, but typically in lower doses and usually accompanied by an aromatase inhibitor to keep estrogen levels under control. Propionate is effective on its own but many do stack it with other anabolic/androgenic steroids for a stronger effect.