Benefits of Testosterone Replacement Therapy

A number of benefits of testosterone replacement therapy have been demonstrated, including effects on mood, energy levels, and libido. Long-term follow-up of testosterone replacement in hypogonadal males and a control group indicates that self-assessment of libido was significantly higher (p<0.0001) in the testosterone-treated group.18 Testosterone replacement has also been shown to enhance libido and the frequency of sexual acts and sleep-related erections.19 Transdermal testosterone replacement therapy, in particular, has been linked to positive effects on fatigue, mood, and sexual function, as well as significant increases in sexual activity.20 More specifically, testosterone replacement therapy has been shown to improve positive mood parameters, such as feelings of wellness and friendliness, while reducing negative mood parameters, such as anger, nervousness, and irritability.21 Testosterone replacement is an effective treatment for some depressive symptoms in hypogonadal men and may effectively augment treatment in selective serotonin reuptake inhibitor (SSRI)-refractory major depression.22 Relative to eugonadal men, hypogonadal men in one study were impaired in their verbal fluency and showed improvement in verbal fluency following testosterone replacement therapy.23

Testosterone replacement therapy is also associated with potentially positive changes in body composition. In hypogonadal men, testosterone replacement therapy has demonstrated a number of effects, including an increase in lean body mass and decrease in body fat,24 an increase in weight,25 and increases in muscle size.26 Parenteral testosterone replacement in hypogonadal men resulted in improved strength and increased hemoglobin compared to controls.27 In another study by Urban and colleagues,28 testosterone administration also increased skeletal muscle protein synthesis and strength in elderly men. Testosterone replacement with transdermal testosterone delivery systems in HIV-infected men with low testosterone levels has been associated with statistically significant gains in lean body mass (p=0.02), increased red cell counts, and improvements in emotional distress.29 Transdermal testosterone has also been administered to HIV-positive women, yielding positive trends in weight gain and quality of life.30

Improvements in bone density have also been shown with testosterone replacement therapy. Increases in spinal bone density have been realized in hypogonadal men,31 with most treated men maintaining bone density above the fracture threshold.32 Testosterone replacement in hypogonadal men improves both trabecular and cortical bone mineral density of the spine, independent of age and type of hypogonadism.33 In addition, a significant increase in paraspinal muscle area has been observed, emphasizing the clinical benefit of adequate replacement therapy for the physical fitness of hypogonadal men. 33

Contraindications to Testosterone Replacement Therapy

Testosterone replacement is contraindicated in men with carcinoma of the breast or known or suspected carcinoma of the prostate, as it may cause rapid growth of these tumors. Hormone therapy is also inappropriate in men with severe benign prostatic hypertrophy (BPH)-related bladder outlet obstruction. Use of testosterone to improve athletic performance or correct short stature is potentially dangerous and inappropriate. In addition, the hormone does not correct ambiguous genitalia resulting from androgen deficiency during fetal development34,35 and should not be administered at dosages high enough to inhibit spermatogenesis.

Safety Issues with Testosterone Replacement

Although testosterone replacement may be indicated in the aging male with documented hypogonadism, this hormone should not be administered with the intent of reversing the aging process in men with normal testosterone levels. Testosterone replacement therapy may be associated with azoospermia, lipid abnormalities, polycythemia, sleep apnea, and the potential for prostate changes.

Azoospermia

The administration of exogenous testosterone as a means of male contraception is under study.36 In these men, azoospermia usually results within approximately 10 weeks of beginning therapy. Rebound of the sperm count to baseline levels occurs within six to 18 months of cessation, and subsequent fertility has been demonstrated.37

Lipid Abnormalities

Physiologic testosterone replacement is known to reduce total cholesterol, low density lipoprotein (LDL), and high density lipoprotein (HDL) levels,24 but the extent to which these parameters are affected by treatment varies considerably between studies. While reductions in HDL did not reach significance in a study by Tenover24 and testosterone replacement was not associated with unfavorable changes in lipid profiles in a separate study by Tan and colleagues,38 research by Anderson and colleagues39 suggests testosterone replacement therapy may result in significant reductions in HDL and elevations in blood viscosity. Some authorities recommend that lipid values be followed closely in men receiving testosterone replacement therapy.

Polycythemia and Sleep Apnea

Polycythemia has been associated with testosterone replacement therapy24 and is correlated with elevated bioavailable testosterone and estradiol levels.40 Physiologic replacement with transdermal testosterone, however, resulted in fewer cases of polycythemia than replacement with testosterone enanthate injections.40 Although the mechanism is unclear, testosterone replacement therapy may also cause or worsen obstructive sleep apnea.

Prostate Changes

Although PSA is not specific for prostate cancer, it is a good surrogate for judging the effects of androgens on the prostate. In one study of testosterone-treated men, PSA rose to normal levels but no higher than in the controls, leading the authors to conclude that testosterone-induced prostate growth should not preclude hypogonadal men from testosterone replacement therapy.41 Indeed, another study indicates that even men who achieved supraphysiologic levels of serum testosterone had no significant changes in PSA levels.42

In a different evaluation, hypogonadal men with normal pretreatment DRE and serum PSA levels who were treated with parenteral testosterone replacement showed no abnormal alterations in PSA or PSA velocity.43 The authors concluded that any significant increases in these parameters should not be attributed to testosterone replacement therapy and should be evaluated. The effects of transdermal testosterone replacement on prostate size and PSA levels in hypogonadal men have also been evaluated.44 Prostate size during therapy with transdermal testosterone was comparable to that reported in normal men, and PSA levels were within the normal range.

Prostate Cancer

There appears to be little association between testosterone replacement therapy and the development of prostate cancer. The etiology of prostate cancer is apparently multifactorial, and dietary, geographic, genetic, and other influences are all thought to play a role in the development of the disease. Recent studies indicate that testosterone levels have no apparent systematic relationship to the incidence of prostate cancer.45,46

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