Testosterone enanthate is a slow-acting injectable form of the androgen testosterone. Following deep intramuscular injection, the drug is designed to provide a sustained release of testosterone into the bloodstream for approximately 2 to 3 weeks. In order to maintain normal physiological levels of testosterone during androgen replacement therapies, injections of testosterone enanthate are usually required at least every two weeks, although more meticulous physicians will administer the drug weekly. As with all testosterone injectables, testosterone enanthate is highly favored by athletes for its ability to promote strong increases in muscle mass and strength. Testosterone enanthate is a modified form of testosterone, where a carboxylic acid ester (enanthoic 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 enanthate is approximately eight days after injection.
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