Testosterone is a key male hormone. It drives libido, affects muscle mass, elevates mood, fights fatigue, adds strength, and improves cognitive ability. Unfortunately, as men age, their testosterone levels begin to decline. This process, called hypogonadism, is a normal part of getting older. But low testosterone levels are more than just an inconvenience of aging. Hypogonadism can cause sexual dysfunction and lead to health problems, including depression and osteoporosis (bone thinning). About 40 percent of men older than 45 suffer from low testosterone levels. After age 45, serum testosterone levels decline about 1 percent per year, and half of men aged 80 and older have low testosterone, according to the American Urological Association.

Slow changes to the body—including loss of muscle mass, reduced body hair, infertility, lowered sex drive, and decreased prostate size—are all symptoms of low testosterone. It is not uncommon to find hypogonadism in patients with infertility. The testicles actually produce testosterone, but the pituitary gland and the brain send signals to the testicles to regulate testosterone production. Although low testosterone levels can result from problems either in the pituitary or in the testicles, the most common cause is testicular dysfunction in the aging male. Less common causes for low serum testosterone are testicular injury, undescended testicles, the results of radiation or chemotherapy, and mumps infection affecting the testicles. Other factors resulting in low serum testosterone can include inflammatory diseases (such as tuberculosis), HIV and AIDS, opiate use, obesity, and type 2 diabetes.

Low testosterone levels not only affect sex drive and sperm function but may also have a negative impact on bone health, red blood cell production, and the development and distribution of muscle and fat.

The most common side effects associated with low testosterone include reduced strength, depressed mood, fatigue, anemia, cognitive problems, and hot flashes. The gold standard for diagnosing hypogonadism is to measure the total testosterone levels in the blood. The normal range for testosterone is 300-1,000 ng/dl (nanograms per deciliter). Anything below 300 is considered abnormal. It is important to draw the blood for testing in the morning, when testosterone levels are typically the highest.

Over the past several years, testosterone replacement therapy (TRT) has increased dramatically, and between 2003 and 2010, testosterone sales jumped more than 500 percent. Although initial studies by the National Institutes of Health could not find any major adverse effects from TRT, side effects can include acne and an increase in circulating red blood cell volume. TRT is contraindicated in men with normal circulating testosterone.

Contrary to common thinking, TRT does not cause prostate cancer. However, if a small, undiagnosed prostate cancer is present, TRT can accelerate the growth of the tumor. Men with a high PSA (prostate-specific antigen) level are not suitable for TRT. Patients receiving treatment need to have their serum testosterone and overall condition monitored on a regular basis. It is recommended that patients who respond well to treatment be monitored every 3-4 months during the first year of treatment. In men over 50 years of age, a prostate examination and PSA testing every 6-12 months is recommended.

Men with confirmed low testosterone levels who choose to undergo treatment have a number of options. Studies show that TRT can help rebuild muscle, restore sexual function, and prevent osteoporosis. Unfortunately, no simple pill exists that can be taken because the oral ingestion of testosterone is extremely toxic to the liver.

Treatment options include injection therapy, wherein testosterone is administered intramuscularly once every two weeks. The disadvantage of injections is that there is a strong surge in the level of serum testosterone shortly after the injection, and this level decreases dramatically at the end of the two-week cycle.

The good news is that a number of topical preparations are available. The testosterone is applied to the skin and is absorbed into the bloodstream at a constant level. A patch can be applied to any hairless surface on a daily basis. The disadvantage of the patch is that it can often cause skin irritation. Several gels that can be applied to the lower abdomen, upper arm, or shoulder are also available. As the gel dries, the testosterone is absorbed through the skin. The gel is less irritating than the patch, but patients should be advised not to wash for several hours after applying the gel and to avoid contact with their children and female partners. On the rare occasions that a pituitary tumor is found as the source of low testosterone, the patient may need surgery or radiation in addition to hormone replacement.

Most importantly, TRT is absolutely contraindicated in men with normal serum testosterone levels. If given in this setting, a patient is no better than a cheating jock attempting to get “juiced” for enhanced physical performance. The results can be disastrous.


Dudley S. Danoff, MD, FACS is the attending urologic surgeon and founder/president of the Cedars-Sinai Medical Center Tower Urology Group in Los Angeles, California. He is the author of Penis Power: The Ultimate Guide To Male Sexual Health (Del Monaco Press, 2011) and Superpotency (Warner Books).

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