What Are the Side Effects of Testosterone Therapy?

Physician-reviewed TRT safety education

What Are the Side Effects of Testosterone Therapy?

TRT can provide meaningful benefits when testosterone deficiency is properly diagnosed, but treatment also has predictable risks that should be discussed before therapy and monitored afterward.

Medically reviewed by Dr. Timothy Mackey
Medical Director · Updated September 2026

Why side effects vary from one man to another

TRT response depends on diagnosis, dose, formulation, achieved testosterone concentrations, age, body composition, sleep, cardiovascular health, medications and fertility goals. A symptom that begins after TRT may be treatment-related, but timing alone does not prove causation.

Major guidelines recommend diagnosing testosterone deficiency from compatible symptoms or signs plus consistently low testosterone concentrations—not from symptoms alone or one isolated result. Proper diagnosis reduces unnecessary exposure to treatment risk.

High hematocrit and erythrocytosis

Testosterone stimulates red-blood-cell production. The American Urological Association recommends measuring hemoglobin and hematocrit before treatment. During TRT, a hematocrit of 54% or higher warrants intervention.

Management may involve reassessing dose and testosterone exposure and evaluating contributors such as sleep apnea, smoking, hypoxia or lung disease. Routine blood donation should not substitute for determining why hematocrit is elevated. See our detailed guide to high hematocrit on TRT.

Blood pressure and fluid retention

FDA requires testosterone products to carry class-wide warnings about increased blood pressure. Men with hypertension or cardiovascular risk should know their baseline blood pressure and have it followed after therapy begins.

Fluid retention can present as ankle swelling or an unexplained rapid change in weight. New or worsening edema deserves evaluation, particularly in patients with cardiac, renal or other relevant medical conditions.

Acne and oily skin

Androgen exposure can increase sebaceous-gland activity and contribute to acne on the face, chest, shoulders or back. Susceptibility varies, and acne does not automatically mean that testosterone is “too high.” Dose, formulation, hormonal fluctuations, skin type and other factors matter.

Persistent or severe acne may require regimen review and standard dermatologic treatment. Read TRT and acne.

Hair changes

Men genetically susceptible to androgenetic alopecia may notice accelerated scalp hair loss. Testosterone can also alter facial or body-hair growth. Hair changes should be considered alongside genetics, age and other medications rather than attributed to one laboratory value.

Breast tenderness or gynecomastia

Breast tenderness or enlargement can occur during testosterone therapy. Estradiol may be relevant, but symptoms should not automatically trigger an aromatase inhibitor. Examination, testosterone exposure, estradiol when appropriate, body composition and other causes should be considered.

Over-suppressing estradiol can itself produce unwanted effects, so treatment should address the clinical problem rather than chase a hormone number.

Fertility suppression and testicular shrinkage

Exogenous testosterone suppresses hypothalamic and pituitary signaling, lowering LH and FSH. Intratesticular testosterone and sperm production can fall substantially, and some men become azoospermic while on TRT. Testicular volume may decrease as well.

This is one of the most important risks to discuss before treatment. Men who want current or future biological children should review alternatives and fertility-preserving strategies. See TRT and fertility.

Prostate and PSA changes

Current evidence has not established that appropriately prescribed TRT causes prostate cancer, but that does not eliminate the need for prostate assessment. PSA can rise modestly in some men after testosterone treatment.

Unexpected PSA changes, concerning examination findings or urinary symptoms should be evaluated rather than dismissed. See TRT and prostate cancer risk.

Sleep apnea and sleep-related symptoms

Men with untreated severe obstructive sleep apnea require particular caution when considering testosterone therapy. Loud snoring, witnessed breathing pauses, morning headaches or persistent daytime sleepiness should prompt evaluation when clinically appropriate.

Sleep apnea can also contribute to elevated hematocrit, making it relevant to more than one aspect of TRT monitoring.

Mood, libido and energy changes

Irritability, altered libido, anxiety, headaches or changes in sleep and energy can occur during treatment, but these symptoms are nonspecific. Testosterone peaks and troughs, stress, depression, thyroid disease, sleep problems and other medications can produce similar complaints.

Severe mood changes, mania, major depression or suicidal thoughts require prompt professional evaluation rather than simply changing a TRT dose.

Injection and formulation-specific side effects

Injections can cause pain, bruising or inflammation at the injection site. Transdermal gels can irritate the skin and may transfer testosterone to another person if product precautions are not followed. Oral testosterone products and other formulations have their own labeling and monitoring requirements.

Formulation choice should therefore consider medical history, lifestyle, adherence, pharmacokinetics and individual adverse-effect patterns—not convenience alone.

What do we know about cardiovascular safety?

The TRAVERSE trial studied middle-aged and older men with hypogonadism and preexisting or high cardiovascular risk. Testosterone therapy was noninferior to placebo for major adverse cardiovascular events in that studied population. This provides important reassurance, but it does not mean TRT is risk-free or appropriate for men without a legitimate indication.

Cardiovascular history, blood pressure and new symptoms remain part of responsible care.

Who may need to delay or avoid TRT?

Important contraindications or reasons for further evaluation can include prostate or breast cancer, concerning unevaluated prostate findings, elevated hematocrit, untreated severe obstructive sleep apnea, uncontrolled heart failure, recent myocardial infarction or stroke, thrombophilia and near-term fertility goals. The decision depends on the individual clinical context.

What should responsible TRT monitoring include?

• Symptoms and treatment benefit rather than laboratory numbers alone.
• Testosterone concentration measured at timing appropriate for the formulation.
• CBC/hematocrit before treatment and periodically afterward.
• Blood pressure because testosterone can increase it.
• Prostate/PSA assessment when appropriate for age and risk.
• Adverse-effect review including skin, breast, edema, urinary, mood and sleep symptoms.
• Fertility goals before treatment and whenever life plans change.

TRT should be reassessed periodically. It should not continue indefinitely merely because a prescription was started years earlier.

Frequently asked questions

What is the most common laboratory side effect of TRT?

An increase in hemoglobin and hematocrit is one of the most important and commonly monitored laboratory changes. AUA guidance recommends intervention when hematocrit reaches 54% or higher during treatment.

Does TRT always cause infertility?

No, but exogenous testosterone can substantially suppress sperm production and can cause azoospermia. Fertility cannot be predicted from testosterone levels alone.

Does TRT cause prostate cancer?

Available evidence has not established that appropriately prescribed TRT causes prostate cancer. Prostate risk assessment and monitoring are still important.

Can TRT raise blood pressure?

Yes. FDA requires class-wide testosterone labeling regarding increased blood pressure, so blood pressure should be considered before and during treatment.

Should side effects be treated by lowering testosterone every time?

No. Management depends on the specific adverse effect, testosterone exposure, formulation and other contributing conditions. Sometimes dose adjustment is appropriate; in other cases the symptom has another cause.

Medical references

• American Urological Association: Testosterone Deficiency Guideline
• Endocrine Society: Testosterone Therapy in Men With Hypogonadism
• FDA: Class-Wide Testosterone Labeling Changes
• TRAVERSE: Cardiovascular Safety of Testosterone-Replacement Therapy

This article is educational and does not replace individualized medical advice, diagnosis or treatment. If symptoms suggest a medical emergency, seek emergency care.