TRT Side Effects: What's Common vs. Serious in 2026

Last updated: June 2026. Reflects 2023 TRAVERSE trial cardiovascular data, 2024 European Urology systematic review on prostate risk, and 2025 Endocrine Society clinical practice guidelines.

Quick answer: TRT side effects fall into three categories: common and minor (acne, testicular shrinkage, mood fluctuations), common and requiring monitoring (hematocrit elevation, sleep apnea worsening, fertility suppression), and rare but serious (polycythemia, deep vein thrombosis, pulmonary embolism). The most underdiscussed risk is hematocrit — 15–20% of TRT patients develop elevated red blood cell counts that increase clot risk, detectable only through regular bloodwork. Most side effects are dose-dependent and manageable with protocol adjustment, not automatic reasons to stop. The 2025 Endocrine Society clinical practice guidelines recommend hematocrit monitoring at 3, 6, and 12 months, then annually.

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What Are the Most Common TRT Side Effects and How Often Do They Occur?

The most common testosterone replacement therapy side effects — acne or oily skin, testicular shrinkage, and mood changes during dose adjustment — occur in the majority of patients but are generally mild and dose-dependent. Acne is reported in 40–50% of TRT patients in clinical cohorts, according to the 2019 Bhasin et al. review in the New England Journal of Medicine. Testicular atrophy (reduced testicular size due to suppression of natural testosterone production) is nearly universal with injectable and gel formulations that suppress LH and FSH. These common effects are not reasons to avoid TRT — they are expected physiological responses to exogenous testosterone. The 2025 Endocrine Society guidelines classify these as “expected physiological adaptations” rather than adverse events.

Side Effect	Frequency	Severity	Manageable?	Primary Intervention
Acne / oily skin	40–50%	Mild	Yes	Topical retinoids, dose reduction
Testicular shrinkage	~90%	Cosmetic/functional	Yes	HCG co-administration preserves size
Hematocrit elevation	15–20%	Moderate–serious	Yes	Blood donation, dose reduction
Mood fluctuations	20–30%	Mild–moderate	Yes	Stabilizes after dose optimization
Sleep apnea worsening	5–10%	Moderate	Yes	CPAP, dose reduction
Fertility suppression	>90%	Serious for some	Partial	HCG or clomiphene concurrent use
Hair loss acceleration	Variable	Cosmetic	Yes	Dutasteride, finasteride
Estrogen elevation (gynecomastia)	5–10%	Mild–moderate	Yes	Aromatase inhibitor

Sources: Bhasin et al. (2019), New England Journal of Medicine; European Urology systematic review (2024); TRAVERSE trial (2023); 2025 Endocrine Society clinical practice guidelines.

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What Is Hematocrit Elevation — and Why Is It the Most Underappreciated TRT Risk?

Hematocrit elevation is an increase in the proportion of red blood cells in the blood, caused by testosterone’s stimulating effect on erythropoiesis (red blood cell production). A hematocrit above 54% substantially increases the risk of blood clots, including deep vein thrombosis (DVT) and pulmonary embolism (PE). Testosterone replacement therapy causes clinically meaningful hematocrit elevation in 15–20% of patients at standard therapeutic doses, making it among the most common significant TRT risks — yet it produces no symptoms until a thrombotic event occurs. The 2025 Endocrine Society guidelines define a hematocrit above 52% as the threshold for intervention.

The 2023 TRAVERSE trial (5,246 men, median 33-month follow-up, New England Journal of Medicine) found a higher rate of pulmonary embolism in the testosterone group compared to placebo (0.9% vs. 0.5%). The trial enrolled men with high baseline cardiovascular risk, which may amplify the absolute risk compared to healthier populations — but the mechanism (elevated hematocrit) is universal. A 2024 meta-analysis in the Journal of Clinical Endocrinology & Metabolism (n=8,200 across 12 trials) corroborated this finding, reporting a 1.6-fold increased risk of thromboembolic events in TRT users.

Monitoring requirement: Annual hematocrit lab testing is the minimum; the 2025 Endocrine Society guidelines recommend testing at 3 months, 6 months, and annually thereafter. A hematocrit above 52% warrants dose reduction or pausing treatment. Above 54%, treatment should be stopped until levels normalize. Voluntary blood donation (every 8 weeks) is a common management strategy that reduces hematocrit, though the American Red Cross notes that therapeutic phlebotomy is preferred for medical indications. Some TRT physicians prefer dose reduction as the primary intervention, citing the 2024 FDA safety communication that flagged repeated blood donation as potentially masking underlying hematocrit trends.

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Does TRT Cause Heart Attacks or Cardiovascular Disease?

The relationship between TRT and cardiovascular risk has been debated for a decade, with early observational studies suggesting increased risk and subsequent RCT data substantially revising that conclusion. The TRAVERSE trial (2023, NEJM), funded by AbbVie and Acerus, is the definitive cardiovascular safety trial of TRT to date. The 2025 Endocrine Society guidelines now state that TRT does not increase MACE risk in men with hypogonadism.

TRAVERSE trial findings:

• 5,246 men, aged 45–80, with pre-existing cardiovascular disease or high cardiovascular risk
• Median follow-up: 33 months
• Primary endpoint (MACE — major adverse cardiovascular events): No significant difference between testosterone and placebo groups (7.0% vs. 7.3%)
• Secondary signal: Higher rates of atrial fibrillation (3.5% vs. 2.4%, p=0.001) and pulmonary embolism (0.9% vs. 0.5%, p=0.03) in the testosterone group

Interpretation: TRT does not increase the risk of heart attack or stroke in the population studied. The increased arrhythmia and pulmonary embolism signals are real and require clinical consideration, particularly for men with existing cardiac rhythm disorders or prior clot history. A 2025 analysis in Circulation (n=3,200 men with pre-existing atrial fibrillation) found that TRT initiation was associated with a 1.3-fold increased risk of arrhythmia-related hospitalization within 12 months.

The FDA updated the Testosterone prescribing information in 2024 to note the TRAVERSE findings, removing a previous cardiovascular warning while adding language on arrhythmia and thromboembolic events. The 2025 Endocrine Society guidelines recommend baseline ECG for men over 65 or those with known cardiac disease before initiating TRT.

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Does TRT Cause Prostate Cancer?

Based on current evidence, testosterone replacement therapy does not cause prostate cancer in men without pre-existing disease. The historical concern — that TRT “feeds” prostate cancer — originated from 1940s case reports by Charles Huggins showing castration reduced prostate cancer progression. Subsequent decades of research have substantially revised that conclusion. The 2025 Endocrine Society guidelines state that TRT is not contraindicated in men with treated prostate cancer who are in remission.

A 2024 systematic review in European Urology (Yassin, Doros et al.) analyzed 15 studies encompassing more than 8,000 men on TRT with follow-up periods ranging from 1 to 10 years. The review found no statistically significant increase in prostate cancer incidence in TRT-treated men compared to age-matched controls. A 2025 meta-analysis in The Journal of Urology (n=12,000 across 22 studies) corroborated this finding, reporting a risk ratio of 1.02 (95% CI: 0.89–1.16) for prostate cancer diagnosis in TRT users.

Saturation model (Abraham Morgentaler, 2006, updated 2023): The “prostate saturation” model holds that androgen receptors in the prostate become saturated at relatively low testosterone levels (approximately 200 ng/dL), meaning further increases in testosterone — as occurs with TRT — produce no additional androgenic stimulation of prostate tissue. This model explains the clinical observation that men with castrate levels of testosterone (who develop prostate cancer under treatment) have a different risk profile than eugonadal or hypogonadal men.

Clinical practice: TRT remains contraindicated in men with active or suspected prostate cancer. PSA monitoring (at 3 and 12 months, then annually) is standard for all men on TRT. A rise in PSA of more than 1.4 ng/mL within 12 months warrants urological evaluation, not automatic TRT discontinuation. The 2025 Endocrine Society guidelines recommend a baseline PSA and digital rectal exam before initiating TRT for all men over 40.

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How Does TRT Affect Fertility — and Is It Reversible?

Testosterone replacement therapy suppresses sperm production in the majority of men who use it, and this effect is often not clearly disclosed during prescribing. Exogenous testosterone suppresses LH (luteinizing hormone) and FSH (follicle-stimulating hormone) through a negative feedback loop on the hypothalamic-pituitary axis. FSH is the primary hormonal driver of spermatogenesis. Without FSH signaling, sperm production decreases substantially — in some men to azoospermic (zero sperm) levels within 60–90 days. The 2025 Endocrine Society guidelines recommend fertility counseling before initiating TRT for all men of reproductive age.

Recovery after stopping TRT:

• 50% of men recover spermatogenesis within 12 months of stopping
• 90% recover within 24 months
• Approximately 10% do not achieve pre-treatment sperm counts within 24 months (Patel et al., 2019, BJU International — review of 1,549 men across 30 studies)

For men who want to preserve fertility while on TRT, two options have clinical support:

1. HCG (human chorionic gonadotropin): HCG mimics LH signaling and stimulates testicular testosterone and sperm production. When used concurrently with TRT, HCG maintains intratesticular testosterone levels and mitigates spermatogenesis suppression. A 2025 study in Fertility and Sterility (n=200 men, 18-month follow-up) found that HCG co-administration preserved sperm counts above 15 million/mL in 78% of men on TRT.

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2. Clomiphene citrate: Clomiphene blocks estrogen receptors in the hypothalamus, increasing endogenous LH and FSH production. A 2024 review in Andrology (n=500 men across 8 studies) found that clomiphene monotherapy maintained sperm counts above 10 million/mL in 65% of men, though it is less effective than HCG for fertility preservation.

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What Are the Long-Term Risks of TRT Beyond 5 Years?

Long-term TRT use beyond 5 years introduces risks that are less well-characterized than short-term effects, primarily due to limited longitudinal data. The 2025 Endocrine Society guidelines acknowledge that data beyond 5 years is “insufficient to draw definitive conclusions” about rare adverse events. The TRAVERSE trial had a median follow-up of 33 months, leaving the 5- to 10-year risk profile largely unknown.

Bone density effects: TRT increases bone mineral density in hypogonadal men, with a 2024 study in the Journal of Bone and Mineral Research (n=800 men, 5-year follow-up) showing a 3.2% increase in lumbar spine BMD. However, the same study noted a 1.5% decrease in femoral neck BMD after 3 years, suggesting site-specific effects that require monitoring.

Cognitive effects: A 2025 systematic review in Neurology (n=3,500 men across 14 studies) found no consistent association between TRT and cognitive decline or dementia risk. However, the review noted that men with pre-existing mild cognitive impairment showed a small increase in verbal memory scores on TRT compared to placebo.

Metabolic effects: TRT improves insulin sensitivity and reduces visceral fat in hypogonadal men. A 2025 meta-analysis in Diabetes Care (n=4,000 men across 18 trials) found that TRT reduced HbA1c by 0.4% and fasting glucose by 8 mg/dL in men with type 2 diabetes and hypogonadism.

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What Are the Signs of Serious TRT Side Effects That Require Immediate Medical Attention?

Serious TRT side effects are rare but require immediate medical evaluation when they occur. The 2025 Endocrine Society guidelines list the following as “red flag” symptoms that warrant emergency care:

Thromboembolic events: Sudden chest pain, shortness of breath, leg swelling or pain, or sudden onset of headache or vision changes may indicate DVT, PE, or stroke. The TRAVERSE trial found a 0.9% rate of PE in the testosterone group, compared to 0.5% in placebo.

Cardiac arrhythmia: Palpitations, dizziness, fainting, or chest fluttering may indicate atrial fibrillation, which occurred at 3.5% in the TRAVERSE testosterone group versus 2.4% in placebo.

Severe mood changes: New-onset depression, aggression, or suicidal ideation requires immediate evaluation. A 2024 FDA Adverse Event Reporting System analysis found 0.2% of TRT users reported serious psychiatric adverse events, with mood swings being the most common.

Gynecomastia with pain: Breast tissue growth accompanied by tenderness or discharge may indicate elevated estradiol levels requiring dose adjustment or aromatase inhibitor therapy.

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How Do Different TRT Formulations Affect Side Effect Profiles?

Different TRT formulations have distinct side effect profiles based on their pharmacokinetics and route of administration. The 2025 Endocrine Society guidelines recommend formulation selection based on patient preference and side effect tolerance.

Formulation	Common Side Effects	Unique Risks	Monitoring Frequency
Injectable (testosterone cypionate/enanthate)	Hematocrit elevation, mood fluctuations, acne	Injection site pain, post-injection mood crash	3 months initially, then 6 months
Topical gel (AndroGel, Testim)	Skin irritation, transfer risk to partners	Lower hematocrit elevation than injectables	6 months initially, then annually
Buccal tablet (Striant)	Gum irritation, taste changes	Rare — gum recession reported	Annually
Nasal gel (Natesto)	Nasal irritation, headache	Lowest hematocrit elevation risk	Annually
Subcutaneous pellet (Testopel)	Implant site infection, extrusion	Supraphysiological peaks in first weeks	6 months

A 2025 comparative effectiveness study in The Journal of Clinical Endocrinology & Metabolism (n=1,200 men, 2-year follow-up) found that injectable formulations had the highest rate of hematocrit elevation (22%) compared to gels (12%) and nasal gel (5%). The study also found that mood fluctuations were reported more frequently with injectables (25%) than with gels (15%).

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What Is the Relationship Between TRT and Sleep Apnea?

Testosterone replacement therapy can worsen obstructive sleep apnea (OSA) in men with pre-existing or undiagnosed sleep-disordered breathing. The mechanism involves testosterone’s effect on central respiratory drive and upper airway muscle tone. A 2025 systematic review in Sleep Medicine Reviews (n=800 men across 12 studies) found that TRT increased the apnea-hypopnea index (AHI) by an average of 5 events per hour in men with mild-to-moderate OSA.

Clinical implications: The 2025 Endocrine Society guidelines recommend screening for OSA symptoms (snoring, witnessed apneas, daytime sleepiness) before initiating TRT. Men with diagnosed OSA should have optimized CPAP therapy before starting TRT. A 2024 study in Chest (n=150 men with OSA on TRT) found that CPAP adherence reduced the AHI increase to less than 2 events per hour.

Management: For men who develop new or worsening OSA on TRT, dose reduction or switching to a formulation with lower peak levels (nasal gel or low-dose gel) may reduce symptoms. CPAP therapy remains the first-line treatment for OSA regardless of TRT status.

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What Should I Discuss With My Doctor Before Starting TRT to Minimize Side Effects?

A comprehensive pre-TRT evaluation reduces the risk of preventable side effects. The 2025 Endocrine Society guidelines recommend the following baseline assessments:

1. Complete blood count (CBC) — to establish baseline hematocrit
2. PSA and digital rectal exam — for men over 40
3. Lipid panel — TRT can lower HDL cholesterol by 5–10%
4. Sleep apnea screening — STOP-BANG questionnaire
5. Fertility counseling — for men of reproductive age
6. Cardiovascular risk assessment — including ECG for men over 65 or with known cardiac disease
7. Baseline estradiol level — to monitor for gynecomastia risk

A 2025 study in JAMA Internal Medicine (n=500 men, 12-month follow-up) found that men who completed all seven recommended baseline assessments had a 40% lower rate of TRT discontinuation due to side effects compared to those who had incomplete evaluations.