Testosterone is the predominant male sex hormone that is produced by the testes beginning in the fetus' eighth week.


In the fetal and embryonic stages of development, testosterone promotes the development of the penis and scrotum and the formation of the structures involved in sperm production.

In the pubescent years (age 9 to 14), testosterone helps in the growth of the testes, body hair, muscles and bones as well as sexual maturation and deepening of the voice.

In adulthood, testosterone may play a part in sexual function, libido, loss of scalp hair, as well as accumulation of abdominal fat.

Between 9 and 14 years of age, the levels of testosterone rise sharply during puberty, which is characterized by enlargement of the testes, pubic and other body hair, muscle and bone growth, deepening of the voice and often acne. If these occurrences are not evident, doctors suggest a number of tests to determine if the male has a condition called hypogonadism.

Testosterone and Hypogonadism

A failure to produce or a decrease in the production of testosterone is called male hypogonadism. Hypogonadism results from failure of the testes to function normally because of genetic defect, illness or injury, or because of abnormal hormonal stimulation of the testes by other glands (e.g., pituitary gland).

Symptoms vary with the age of the male as well as the specific cause of hypogonadism. By the 12th week of gestation, male genitalia may not form fully or properly. During childhood, the boy may begin puberty late or not at all and exhibit reduced growth of male organs and body hair. Additionally, the development of muscle and strength may be below average and retention of a high-pitched pre-pubescent voice may be evident. In an adult, the effects of hypogonadism may include diminished sexual drive, potency, sperm production and overall body strength.

An accurate diagnosis of hypogonadism requires a detailed history, a physical exam and hormonal studies. Chromosomal analysis may determine the specific cause. Testicular biopsy and semen analysis determine sperm production, identify impaired sperm formation and assess the effect of low levels of testosterone. Treatment for hypogonadism depends on the underlying cause and consists of testosterone replacement therapy.

Testosterone and Aging

As men age, their testosterone levels may slowly decline. This occurrence has been called "viripause", "andropause" or "male menopause."

This menopause may be caused by the testosterone receptors becoming less receptive, while the amount of free testosterone in the body decreases. The decrease is due to an increase in a blood protein that binds with the hormone, rendering it useless.

The gradual fall in the testosterone levels (from 30 to 40 percent) is common in men between the ages of 48 and 70. As testosterone levels drop, men may experience a loss in muscle strength and function, increase in body fat, decrease in body density and a decrease in sexual function and drive. Of course, your physician first needs to rule out other medical causes for those changes.

Testosterone Replacement Therapy in Men

Testosterone replacement therapy can be used to treat hypogonadism in boys and men. However, some scientists believe that testosterone replacement therapy may help counter the effects of declining testosterone levels in "normal-testosterone producing" older men.

Testosterone replacement therapy can be administered orally, via injection or transdermally (applied as a patch).

In the mid 1990s, the FDA approved two transdermal patches (Testoderm and Androderm) that help men with hypogonadism boost their low testosterone levels. The patch releases a steady supply of the hormone into the blood.

The side effects of testosterone can include agitation, rapid heart rate, nervousness, and polycythemia (excess of red blood cells), and prostate gland growth. It is recommended that a prostate exam and prostate-specific antigen (PSA) levels be checked before and after therapy to help rule out prostate cancer.

Supplementing testosterone to increase athletic performance is harmful. Supplementation can cause abnormal bone growth, premature growth stoppage, nausea, gastrointestinal problems, blood clots, headaches, anxiety, depression, high cholesterol levels, and over a long period of misuse, it may suppress normal testosterone production.

Testosterone in Women

There is increasing awareness that many women experience symptoms of androgen deficiency after either natural or surgical menopause. The predominant complaint of affected women is less sexual desire and diminished libido.

Many women experiencing the clinical symptoms of androgen deficiency and low free testosterone levels respond well to testosterone replacement therapy, or menopausal androgen replacement therapy (MART). However, the efficacy of MART in alleviating these symptoms compared to traditional estrogen and progestin hormone replacement therapy (HRT) remains controversial.

Additional concerns are related to the risks of developing endometrial hyperplasia and breast cancer when MART is used in conjunction with estrogens. In general, the safety profile of MART seems to be acceptable when dosing avoids supraphysiologic testosterone levels. However, in comparison to the many years and experience in evaluating the effects of estrogens, studies of androgen effects are still at a preliminary stage.


Testosterone replacement therapy for men and women as it relates to the aging process and body maintenance is far from the standard practice in the U.S. Whether science can establish a role for this hormone in the treatment of men and women is a question that awaits further research.