Androstenedione (Δ4-Androstenedione, 4-androstene-3,17-dione or 17-ketotestosterone) is an endogenous androgen steroid hormone and intermediate in the biosynthesis of testosterone from dehydroepiandrosterone (DHEA). In turn, Androstenedione is also a precursor of dihydrotestosterone (DHT), estrogens such as estradiol and estrone, and the neurosteroid 3α-androstanediol. Androstenedione is used to increase the production of the hormone testosterone to enhance athletic performance, increase energy, keep red blood cells healthy, enhance recovery and growth from exercise, and increase sexual desire and performance. Androstenedione has been shown to increase serum testosterone levels over an eight-hour period in men when taken as a single oral dose of 300 mg per day, but a dose of 100 mg had no significant effect on serum testosterone. However, serum levels of estradiol increased following both the 100 mg and 300 mg doses. The study also reported that the serum level of estrogens and testosterone produced varied widely among individuals. Androstenedione is currently used as a nutritional supplement to grow bigger muscles and stronger bones. This implies that androstenedione may have anabolic properties. Even though it has not been convincingly demonstrated yet that androstenedione is an anabolic steroid, its anabolic properties are likely based on its proven ability to increase testosterone levels. The role of testosterone in building stronger muscles and bones is widely accepted. Thus, high doses of testosterone-boosting drugs combined with strength training have been shown to increase muscle size and strength even in normal young men. This confirms what thousands of athletes who take anabolic steroids have known for decades. Yet androstenedione is different from testosterone-boosting drugs in a number of important aspects. To begin with, androstenedione is a naturally occurring substance that is produced by the body itself. In contrast to synthetic anabolic steroids, androstenedione is right at home in the human body, and perfectly complements the complex hormonal network in the body. Information about possible side effects and risks of androstenedione is very limited. Also, recent studies show that the drug's actions don't support manufacturer's claims. While a few individuals have shown increased levels of testosterone, most failed to achieve increases in blood testosterone levels. Initial medical research has raised concerns about this supplement's safety. Doctors worry that androstenedione may increase the risk of heart disease or liver cancer. In addition, research also associates androstenedione use with increases in estradiol, a female estrogen.