Testosterone Replacement Therapy

What is testosterone?

Testosterone is a hormone produced primarily in the testicles. Testosterone helps maintain men's:

  • Bone density
  • Fat distribution
  • Muscle strength and mass
  • Facial and body hair
  • Red blood cell production
  • Sex drive
  • Sperm production
  • Changes in sexual function. This may include reduced sexual desire, fewer spontaneous erections — such as during sleep — and infertility.
  • Changes in sleep patterns. Sometimes low testosterone causes insomnia or other sleep disturbances.
  • Physical changes. Various physical changes are possible, including increased body fat, reduced muscle bulk and strength, and decreased bone density. Swollen or tender breasts (gynecomastia) and body hair loss are possible. You may have less energy than you used to.
  • Emotional changes. Low testosterone may contribute to a decrease in motivation or self-confidence. You may feel sad or depressed, or have trouble concentrating or remembering things.

What happens to testosterone levels with age?

Testosterone levels generally peak during adolescence and early adulthood. As you get older, your testosterone level gradually declines — typically about 1 percent a year after age 30 or 40. It is important to determine in older men if a low testosterone level is simply due to the decline of normal aging or if it is due to a disease (hypogonadism).
Hypogonadism is a disease in which the body is unable to produce normal amounts of testosterone due to a problem with the testicles or with the pituitary gland that controls the testicles. Testosterone replacement therapy can improve the signs and symptoms of low testosterone in these men. Doctors may prescribe testosterone as injections, pellets, patches or gels.