Testosterone is a hormone that acts as the primary sex hormone in men. It is produced by the male testicles and the female ovaries. Testosterone levels in men increase during and after puberty, dropping again after about age 40. Testosterone causes the deeper voice, bigger muscles, body hair, and other primarily male features. Follow the links below to find WebMD's comprehensive coverage about what testosterone is, what it does in the body, what levels are normal, and much more.
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Slideshows & Images
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Slideshow: Effects of Low Testosterone
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Take this quiz and see how much you know about aging and low testosterone in men. What do you know about low T and how it can affect you as you get older?