Testosterone is the main sex hormone found in men. It controls male physical features. The testes (testicles) make testosterone. Women have testosterone too but in much smaller amounts than in men. When you think of testosterone, what comes to mind? Macho men? Aggressive, impatient, type A behavior? Road rage? Violence?Testosterone's role in bad behavior is largely a myth. What's more, testosterone plays other important roles in health and disease that may surprise you. For example, did you know that testosterone is a key player in prostate cancer? Or, that women need testosterone, too? There's more to testosterone than guys behaving badly. Adolescent boys with too little testosterone may not experience normal masculinization. For example, the genitals may not enlarge, facial and body hair may be scant and the voice may not deepen normally. Testosterone may also help maintain normal mood. There may be other important functions of this hormone that have not yet been discovered. Signals sent from the brain to the pituitary gland at the base of the brain control the production of testosterone in men. The pituitary gland then relays signals to the testes to produce testosterone. A "feedback loop" closely regulates the amount of hormone in the blood. When testosterone levels rise too high, the brain sends signals to the pituitary to reduce production. If you thought testosterone was only important in men, you'd be mistaken. Testosterone is produced in the ovaries and adrenal gland. It's one of several androgens (male sex hormones) in females. These hormones are thought to have important effects on:The proper balance between testosterone (along with other androgens) and estrogen is important for the ovaries to work normally. While the specifics are uncertain, it's possible that androgens also play an important role in normal brain function (including mood, sex drive and cognitive function). Testosterone is synthesized in the body from cholesterol. But having high cholesterol doesn't mean your testosterone will be high. Testosterone levels are too carefully controlled by the pituitary gland in the brain for that to occur. Having too much naturally-occurring testosterone is not a common problem among men. That may surprise you given what people might consider obvious evidence of testosterone excess: road rage, fighting among fathers at Little League games and sexual promiscuity. Part of this may be due to the difficulty defining "normal" testosterone levels and "normal" behavior. Blood levels of testosterone vary dramatically over time and even during the course of a day. In addition, what may seem like a symptom of testosterone excess (see below) may actually be unrelated to this hormone. In fact, most of what we know about abnormally high testosterone levels in men comes from athletes who use anabolic steroids, testosterone or related hormones to increase muscle mass and athletic performance