It is estimated that four to five million American men may not produce enough testosterone. Most discouraging, research finds that most men know very little about testosterone, the potential consequences of having low testosterone levels, and the availability of therapies to increase testosterone and overall health. A 1998 survey completed by Roper Starch Worldwide of 1,000 men found that 68 percent of participants could not name a symptom or condition associated with low testosterone. In addition, half of the participants admitted some knowledge of hormone replacement therapy, but only seven percent knew that it could be used in men.

This guide seeks to improve your awareness of testosterone, testosterone deficiency, and testosterone replacement therapy. Section 1, Testosterone Overview, provides comprehensive information on the hormone, its function, the diagnosis of low testosterone, and other related factors. Section 2, Benefits and of Testosterone Replacement Therapy (TRT) discusses some of the physical and psychological benefits associated with restoring testosterone. Section 3, Treatments for Low Testosterone, outlines treatment options that are available to increase testosterone levels. Section 4, Potential Risks of Testosterone Replacement Therapy, outlines the risks associated with prolonged testosterone therapy. Section 5, Overview of Clinical Trials, presents highlights of recent clinical studies evaluating testosterone and testosterone replacement therapy. Finally, Section 6, Frequently Asked Questions and Section 7, Glossary of Terms provide additional information and resources.

The Effects of Aging on Testosterone Production — Andropause

As men age, their ability to produce testosterone declines. Also, some men's production of LH decreases with aging, which lowers testosterone production. Moreover, a protein that binds up and holds onto testosterone called sex hormone binding globulin (SHBG) increases in older men. This reduces the amount of free (unbound) testosterone in the blood that is available to tissues, such as muscles. Aging also causes changes in the daily cycle of testosterone production. For example, younger men show a peak of testosterone in the morning, but this finding is blunted in older men.

The decrease in testosterone production as men age and symptoms associated with testosterone deficiency are sometimes referred to as andropause.

Physical Symptoms Related to Low Testosterone

Signs of low testosterone in men may include decreased sex drive, poor erections by the penis [erectile dysfunction (ED)], lowered sperm count and reduced fertility, or increased breast size. Men also may have symptoms similar to those seen during menopause in women — hot flashes, increased irritability, inability to concentrate, and depression. Some men may have a prolonged and severe decrease in testosterone production. As a result, they may experience loss of body hair and reduced muscle mass, their bones may be more brittle and prone to fracture, and their testes may become smaller and softer. In younger men, low testosterone production may reduce the development of body and facial hair, muscle mass, and genitals. In addition, their voices also may fail to deepen.

Conditions That Could Cause Low Testosterone

There are a number of specific medical conditions that can cause low testosterone. Often, such conditions are most evident in younger men and men with extremely low testosterone levels. Some of these conditions are associated with diseases or abnormalities of the testes, pituitary gland and hypothalamus. Other men experience low testosterone levels as a result of various genetic factors.