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Description Androstenedione is a "pro-hormone," meaning that it is an inactive precursor of another hormone – in this case, a precursor of both female (estrogen) hormones and male (testosterone) hormones. Androstenedione, a steroid hormone, is a natural substance made in the adrenal gland and the gonads. It is also found in small amounts in some plants. Androstenedione is synthesized in the adrenal gland and gonads from dehydroepiandrosterone. It is metabolized by the enzyme 17 beta-hydroxy steroid dehydrogenase to testosterone, and by the aromatase enzyme complex to estrone. Estrone is metabolized to estradiol. What It Does It is said that supplemental androstenedione can significantly increase blood testosterone levels and build muscle. Androstenedione is metabolized into testosterone in both men and women, and is reported to increase nitrogen preservation resulting in increased muscle mass. In the body, "andro" becomes active upon conversion to testosterone - the major "male" hormone responsible for muscle growth and other male characteristics such as growth of facial hair and development of a deep voice. Higher levels of testosterone are thought to help athletes exercise more intensely and recover faster. Thus