What is Testosterone? Image

Testosterone is a sex hormone that plays key roles in male development. Like all hormones, testosterone is a chemical produced by glands and then secreted to travel throughout the body. Although it is produced by both sexes, men produce considerably more testosterone than women, particularly during puberty.

The Importance of Testosterone

Testosterone is needed for normal growth and development in both boys and girls throughout childhood and early adulthood. In boys, testosterone production peaks during puberty when it contributes to many of the hallmarks of male development, including:

  • Change in voice
  • Development of muscle tissue
  • Growth of hair on face and body
  • Growth of bones
  • Onset of sex drive
  • Production of sperm.

Biology of Testosterone - Testosterone Target Organs

For adult men, testosterone is important to maintain fertility, muscle mass and sex drive.

The Production of Testosterone: Women vs. Men

In males, the testes (which are the male reproductive glands) are the primary producers of testosterone. In women, approximately half of the testosterone in the body is produced in the ovaries–which are the female reproductive glands–and the other half is produced in the adrenal gland. While a typical adult male produces between 6 and 8 mg of testosterone each day, an adult woman produces around 0.5 mg.

Testosterone Levels

In grown men, testosterone levels are frequently not as high as during development, and levels generally continue to decrease with age. This decline is typically not significant enough to affect overall health. However, particularly after age 40, some men may experience consequences of reduced testosterone.

Effects of low testosterone in older men can include:

  • Changes in mood
  • Erectile dysfunction
  • Fatigue
  • Low libido
  • Muscle atrophy.

Low testosterone has also been linked to high blood pressure and diabetes, but it remains unclear if low testosterone increases risk to these conditions, or if the conditions are frequently found together for other reasons.

Testosterone Replacement Therapy

For men with abnormally low testosterone levels (e.g. from a medical condition or injury), testosterone replacement therapy is available to bring their levels back into normal range. However, men experiencing normal reductions in testosterone levels as the result of aging may not benefit from this therapy, and could put themselves at risk for complications of high testosterone. A doctor can perform a testosterone test to determine if levels are within normal range before making recommendations on possible treatments.

Women also experience a decrease in testosterone with aging, especially after menopause. This decrease has been linked to a reduced sex drive and possibly an increased risk of cardiovascular disease.


Mayo Foundation for Medical Education and Research staff. (2009). Male menopause: Myth or reality? Retrieved January 12, 2010 from the Mayo Clinic Web site: http://www.mayoclinic.com/health/male-menopause/MC00058.

Mayo Foundation for Medical Education and Research staff. (2008). Testosterone therapy: Can is help older men feel young again? Retrieved January 12, 2010 from the Mayo Clinic Web site: http://www.mayoclinic.com/health/testosterone-therapy/MC00030.

Morgentaler, A. (2008). Testosterone and diabetes — An important link? Retrieved January 12, 2010 from the Diabetes Health Web site: http://www.diabeteshealth.com/read/2008/12/15/6018/testosterone-and-diabetesan-important-link/.

Sindair Intimacy Institute. (2002). Estrogen and testosterone hormones. Retrieved January 12, 2010 from the Discovery Health Web site: http://health.discovery.com/centers/sex/sexpedia/hormone.html.

State of Victoria staff. (2009). Androgen deficiency in men. Retrieved January 12, 2010, from the Better Health Channel Web site: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Androgen_deficiency.