What is testosterone?  Updated: 4/11/2007 5:47 pm Testosterone
(tess-TOSS-tuh-roan), the primary male hormone, is produced in
the testes (TESS-teez), and governs many functions throughout
your body. It's necessary for sex drive in both males and
females, though women have much smaller amounts. In men,
testosterone is responsible for normal development of sex
organs, the production of sperm, and male characteristics like
facial hair and a deep voice. Testosterone also affects bone and
muscle growth, the prostate, and your central nervous system.
Levels tend to peak early in the morning, and fall to their
lowest point in late evening. As you age, testosterone
production gradually declines. By age 60, some men's levels
become so low as to cause fatigue, lack of sex drive, and the
inability to get or maintain an erection. Irritability,
decreased muscle mass, reduction in facial hair, and increased
breast size are other possible symptoms. Some younger men may
also experience an abnormal drop in testosterone, a con