Testosterone replacement therapy (TRT) is usually well tolerated as long as testosterone is kept within normal, physiologic levels. Side effects of testosterone therapy are generally mild. However, it is important for you and your physician to be aware of the following potential side effects. Many of the side effects may be mitigated by avoiding the most common testosterone replacement mistakes and by following-up regularly with your physician.
Also, it should be noted that the FDA has recently decided to require manufacturers to include labeling that informs patients about the possible increased risk of heart attacks and stroke in patient taking testosterone.
Page Table of Contents
Side Effects of Testosterone Therapy
1. Increased Levels of Red Blood Cells
One of the potential side effects of testosterone therapy is an increase in red blood cell count beyond what is healthy for the body. Testosterone promotes the synthesis of red blood cells. Thus, taking exogenous testosterone increases red blood cell count.
Red blood cells contribute to the viscosity of blood. More red blood cells lead to thicker, more viscous blood. In certain cases, red blood cell count may become too high, leading to overly viscous blood. Overly viscous blood increases your risk of forming blood clots, which can subsequently lead to a heart attack and/or stroke.
A measure of your red blood cell count can alert your physician of this problem. Your doctor can then correct the problem by temporarily interrupting the dose, changing the method of administration, or performing a simple withdrawal of blood, if necessary. It is important to note that injectable testosterone is more likely to cause an increased red blood cell count than any of the other forms of testosterone.1-4 Men using injectable testosterone should be vigilant in monitoring for this particular problem. Lowering the injectable dosage and shortening the time between injections may potentially reduce the possibility of this side effect.
2. Worsening of Sleep Apnea.
Testosterone therapy may increase your odds of getting sleep apnea, or it may worsen sleep apnea if you already suffer from the disease.5-7 Sleep apnea is a serious condition that causes you to lose oxygen supply intermittently while you sleep. It is important to know the signs of sleep apnea and report them to your doctor both before starting therapy and after beginning therapy.
3. Infertility
Testosterone therapy suppresses the natural production of testosterone by the testes. Since sperm production requires high levels of testosterone within the testes and TRT suppresses testosterone production by the testes, TRT reduces sperm production. In most men, it reduces sperm production to levels below what is necessary for fertility. As a result, most men on testosterone therapy are infertile. Diminished testicular size also may occur because of the down-regulation of the gonadotropins.
While this side effect may not concern certain men, men looking to conceive a child or remain fertile must be aware of this potential side effect of TRT. While infertility is usually reversible, the testosterone dosage must either be decreased or TRT must be stopped all together.4
Men looking to maintain fertility may discuss adding human chorionic gonadotropin (HCG) to their TRT regimen with their physician. In men, HCG stimulates testosterone production by the testes, leading to sperm production.
4. Gynecomastia
One of the more unappealing potential side effects of testosterone therapy is gynecomastia. Gynecomastia is male breast enlargement due to benign (non-cancerous) breast tissue growth. While it is benign, it is aesthetically unappealing. It is related to aromatization of testosterone into estradiol in peripheral fat and muscle tissue. This aromatization causes the breast tissue to swell. Unfortunately, medical treatment of gynecomastia that has persisted beyond a year is often ineffective.
5. Small Decrease in HDL Cholesterol
Testosterone therapy may adversely affect cholesterol levels, slightly lowering HDL cholesterol and slightly raising LDL cholesterol. Most cases of adverse affects to cholesterol deal with supraphysiological doses of testosterone, not replacement doses. Therefore, the risk of cholesterol related side effects of testosterone therapy is modest.
6. Fluid Retention in the Extremities
Fluid retention may occur in the arms and legs at the beginning of therapy. It generally resolves after the first few months of treatment.
FDA Statements on Side Effects of Testosterone Therapy
In 2014 and 2015, the FDA released statements on testosterone replacement therapy. The first statement released on January 31st, 2014 said that it is investigating the risk of stroke, heart attack, and death in men taking FDA-approved testosterone products. This statement was in response to two observational studies that observed an increased risk of stroke and heart attack in men on testosterone therapy.8,9
On March 3rd, 2015, the FDA released a follow-up statement to its initial 2014 statement. This statements states the that testosterone replacement therapy is only for men with low testosterone levels due to certain medical conditions. It also requires manufacturers to add labeling to inform patients about the possible increased risk of heart attacks and stroke in patient taking testosterone. The FDA statement includes the following summary:
“The U.S. Food and Drug Administration (FDA) cautions that prescription testosterone products are approved only for men who have low testosterone levels caused by certain medical conditions. The benefit and safety of these medications have not been established for the treatment of low testosterone levels due to aging, even if a man’s symptoms seem related to low testosterone. We are requiring that the manufacturers of all approved prescription testosterone products change their labeling to clarify the approved uses of these medications. We are also requiring these manufacturers to add information to the labeling about a possible increased risk of heart attacks and strokes in patients taking testosterone. Health care professionals should prescribe testosterone therapy only for men with low testosterone levels caused by certain medical conditions and confirmed by laboratory tests.”
Interestingly, a new meta-analysis (Testosterone Therapy and Cardiovascular Risk: Advances and Controversies) in the Mayo Clinic Proceedings published during this FDA review says there is no evidence of increased cardiovascular risks. This meta-analysis is the largest to date, and it revealed no increase in cardiovascular risks in men who received testosterone. It also revealed reduced cardiovascular risk among those men with metabolic disease. This analysis contradicts the findings of the two studies that led the FDA to begin a review of the risk of cardiovascular disease side effects of testosterone therapy.10
Currently, there is no clear consensus on the whether or not testosterone therapy increase the risk of heart attack or stroke.
Contraindications of Testosterone Therapy
In certain situations, testosterone therapy should not be initiated or continued. The Endocrine Society Clinical Practical Guidelines detail the conditions in which testosterone administration is associated with a high risk of adverse outcome and in which testosterone should not be administered:11
| Very high risk of serious adverse outcomes |
| Metastatic prostate cancer |
| Breast cancer |
| Moderate to high risk of adverse outcomes |
| Unevaluated prostate nodule or induration |
| PSA >4 ng/ml (>3 ng/ml in individuals at high risk for prostate cancer, such as African-Americans or men with first-degree relatives who have prostate cancer) |
| Hematocrit >50% |
| Severe lower urinary tract symptoms associated with benign prostatic hypertrophy as indicated by AUA/IPSS >19 |
| Uncontrolled or poorly controlled congestive heart failure |
Other Potential Concerns Regarding Testosterone Therapy
1. TRT does not appear to cause or worsen prostate cancer.
For years, physicians have worried that one of the potential side effects of testosterone therapy would be the causing or worsening of prostate cancer. Fortunately, most studies agree that testosterone does not induce a development of malignant prostate cells.12-15 Furthermore, most studies have found no relation between testosterone levels and the likelihood of developing prostate carcinomas.5,6,16,17
Current available information suggests that even men with prostate cancer can safely be treated with TRT, although the Endocrine Society’s Guidelines do not recommend administering therapy to men with metastatic prostate cancer.4 Nevertheless, more long-term studies are necessary to fully understand side effects of testosterone therapy on the prostate.
2. TRT does not cause benign prostatic hyperplasia (BPH).
Testosterone therapy may increase the prostate’s size, but the evidence shows that it does not cause or worsen symptoms of benign prostatic hyperplasia (BPH). The increase in the prostate typically occurs in the first six months and is relative to the amount of testosterone taken. The increase in size of the prostate usually is equivalent to that of men with normal testosterone levels. Fortunately, the increase in size does not typically increase urinating problems.18,19 Urine flow rates, post-urinating residual urine volumes, and prostate voiding symptoms, however, do not change significantly.18,19
Final Notes
As can be seen, it is important to understand that like any prescription-based therapy potential side effects of testosterone therapy exist. Nevertheless, side effects are generally mild as long as testosterone is kept within normal, physiologic levels. Keeping testosterone levels comes down to your physician and you. Your physician is responsible for designing a regimen and continually following-up on your progress. You are responsible for following the regimen and following up with and providing feedback to your physician. Ultimately, treatment comes down to the individual’s personal problems with low testosterone.
EMG’s TRT Homepage: Testosterone Replacement Therapy
External Resources:
Updated: April 22nd, 2015
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