Side Effects of Testosterone Replacement Therapy

Men's Lifestyle, Testosterone Therapy

Testosterone replacement therapy is an effective and well-studied treatment for hypogonadism, but like any medical intervention, it carries potential side effects. Some are common and manageable; others are serious enough that they require monitoring and, in some cases, treatment adjustment. Understanding what side effects to watch for, how they occur mechanically, and what can be done about them is a core part of informed consent before starting TRT. This article covers the full landscape of TRT side effects, separating myth from clinical reality. For a broader overview of what TRT is and how it is administered, see our guide on testosterone replacement therapy.

Erythrocytosis (Elevated Red Blood Cell Count)

Elevated hematocrit (erythrocytosis) is the most commonly observed clinically significant side effect of TRT. Testosterone stimulates erythropoietin production in the kidneys, which in turn drives red blood cell production in the bone marrow. This is why TRT can improve energy and exercise capacity in some men; more red blood cells means more oxygen-carrying capacity. However, when hematocrit rises excessively, usually above 52 to 54 percent, blood viscosity increases, raising the risk of blood clots, stroke, and cardiovascular events ( 1 ).

Monitoring hematocrit at baseline, three months after starting TRT, and every six to twelve months thereafter is standard practice. If levels rise too high, options include dose reduction, switching to a delivery method with a flatter pharmacokinetic profile, increasing hydration, or therapeutic phlebotomy (blood donation or blood removal). Erythrocytosis is generally manageable with appropriate monitoring.

Infertility and Testicular Atrophy

Exogenous testosterone suppresses the HPG axis, reducing LH and FSH signals to the testes. The practical result is a reduction in sperm production (oligospermia or azoospermia) and testicular atrophy over time. For men not seeking to conceive, testicular shrinkage is primarily cosmetic and does not affect overall health. For men who want to preserve fertility, this is a critical consideration before starting TRT ( 2 ).

Human chorionic gonadotropin (hCG) can be used alongside TRT to maintain testicular volume and preserve some degree of sperm production by mimicking the action of LH. For men who prioritize fertility, alternatives to TRT such as clomiphene citrate may be more appropriate. For a full discussion, see our article on TRT and fertility.

Acne and Oily Skin

Androgens stimulate sebaceous (oil) glands in the skin. Increased testosterone, whether from TRT or naturally elevated levels, can increase sebum production, leading to oily skin and, in some men, acne. This is more common in younger men and men using higher doses. The severity varies widely: some men notice mild changes, while others develop significant acne on the face, chest, or back ( 3 ).

Management options include topical treatments (benzoyl peroxide, retinoids), dietary modification (reducing high-glycemic foods and dairy), and in some cases dose adjustment. Switching delivery methods, since some evidence suggests injections with high peak levels may cause more acne than preparations with flatter profiles, can also help.

Estrogen-Related Side Effects

Testosterone is converted to estradiol in the body by the aromatase enzyme, which is present in fat tissue, liver, muscle, and other tissues. Elevated estradiol can cause symptoms including breast tissue growth (gynecomastia), water retention, moodiness, and reduced libido. These effects are more common in men who carry more body fat (more aromatase activity) or those receiving higher testosterone doses ( 1 ).

Aromatase inhibitors (AIs) such as anastrozole are sometimes used to manage elevated estradiol. However, suppressing estradiol too aggressively can cause joint pain, decreased bone density, reduced libido, and worsened lipid profiles, because men need some estradiol for bone health and cardiovascular function. Estrogen management on TRT requires careful titration, not blanket suppression.

Sleep Apnea

Testosterone therapy may worsen pre-existing sleep apnea or, in predisposed individuals, contribute to its development. The mechanism is not fully established but may involve effects on upper airway musculature and the central respiratory drive. Men with known sleep apnea should have it treated before or alongside TRT, and any new development of snoring, apneic episodes, or daytime fatigue on TRT should be evaluated ( 2 ).

Prostate Health

For decades, there was concern that TRT could accelerate prostate cancer growth, based on the historical observation that castration (which eliminates testosterone) reduces prostate cancer progression. More recent research and major clinical guideline updates have substantially revised this view. TRT at physiological levels does not appear to cause prostate cancer in men without pre-existing disease ( 1 ), ( 3 ).

However, TRT is contraindicated in men with active prostate cancer. In men with a history of low-risk prostate cancer who have been treated successfully, the decision to use TRT is individualized and requires specialist input. Routine PSA monitoring is standard during TRT. A rise in PSA on TRT should be investigated.

Cardiovascular Considerations

Cardiovascular safety of TRT has been an area of significant research and debate. The TRAVERSE trial, a large randomized controlled trial published in 2023, found that testosterone therapy in men with hypogonadism and elevated cardiovascular risk did not significantly increase major adverse cardiovascular events compared to placebo, though there were modest increases in atrial fibrillation and some other secondary outcomes ( 1 ). This updated evidence is now incorporated into clinical guidelines.

The cardiovascular risk profile of an individual patient, including existing conditions, medications, and hematocrit response, remains an important part of TRT risk-benefit assessment.

Common Myths About TRT Side Effects

A persistent myth is that TRT inevitably causes heart attacks. This arose partly from a 2010 study with significant methodological limitations that was later widely criticized. The current evidence from well-designed trials does not support the idea that properly monitored, physiological-dose TRT causes heart attacks in otherwise healthy men.

Another myth is that TRT always causes rage or aggression. Supraphysiological doses, as used in non-medical anabolic steroid abuse, can influence mood dysregulation. Physiological replacement therapy aimed at restoring normal levels does not typically cause aggression; in fact, many men on TRT report calmer, more stable mood.

When to See a Provider

If you are on TRT and experiencing any new or worsening symptoms, scheduled lab monitoring is essential. Do not adjust doses or stop TRT abruptly without provider guidance. Side effects are manageable with appropriate clinical oversight, and most men on TRT do not experience significant problems when treatment is properly supervised.

If you are considering TRT and want to understand the full risk-benefit picture, speaking with a men’s health provider is the right first step. A thorough evaluation will help determine whether TRT is appropriate and what monitoring plan should be in place.

Emergency Notice: If you or someone else is experiencing a medical emergency, call 911 immediately. The information on this site is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.