Testosterone propionate is a commonly manufactured injectable form of the primary male androgen testosterone.The added propionate ester will slow the rate in which testosterone is released from the injection site, but only for a few days. Testosterone propionate is, therefore, comparatively much faster-acting than other testosterone esters such as cypionate or enanthate, and requires a much more frequent dosing schedule. By most accounts testosterone propionate is an older and cruder form of injectable testosterone, made obsolete by the slower-acting and more comfortable esters that were developed subsequent to it. Still, those who are not bothered by the frequent injection schedule find testosterone propionate every bit as acceptable. As an injectable testosterone, it is a powerful mass-building drug, capable of producing rapid gains in both muscle size and strength. Testosterone propionate is a modified form of testosterone, where a carboxylic acid ester (propionic acid) has been attached to the 17-beta hydroxyl group. The half-life of testosterone propionate is approximately two days after injection.

Testosterone is readily aromatized in the body to estradiol (estrogen). The aromatase (estrogen synthetase) enzyme is responsible for this metabolism of testosterone. Elevated estrogen levels can cause side effects such as increased water retention, body fat gain, and gynecomastia. Elevated levels of testosterone are likely to produce androgenic side effects including oily skin, acne, and body/facial hair growth. Men with a genetic predisposition for hair loss (androgenetic alopecia) may notice accelerated male pattern balding. Testosterone propionate is often regarded as a painful injection. This is due to the very short carbon chain of the propionic acid ester, which can be irritating to tissues at the site of injection. Many sensitive individuals choose to stay away from this steroid completely, their bodies reacting with a pronounced soreness and low-grade fever that may last for a few days after each injection.