Testosterone replacement therapy is one of the most-prescribed and most-debated treatments in men’s health. With the publication of the TRAVERSE trial in 2023, the long-running cardiovascular controversy was substantially clarified, but the broader question of TRT side effects — what is common, what is rare but serious, and what the long-term risks actually look like — still confuses men starting treatment. Most side effects are predictable, monitorable, and manageable. A few are serious enough to warrant specific vigilance.
Common Side Effects
Acne and oily skin are among the most common cosmetic effects, particularly in younger men or those starting at the upper end of the dosing range. They typically appear within the first 4 to 8 weeks and improve with dose adjustment or topical therapy. Increased body hair growth and accelerated male-pattern baldness in genetically susceptible men also occur because dihydrotestosterone (DHT) metabolites rise with TRT.
Fluid retention, mild ankle swelling, and modest weight gain (often as lean mass) are common in the first few months. Mood changes — most commonly improvement, but occasionally irritability or sleep disturbance — are reported. Site-specific issues depend on formulation: injection-site soreness with IM testosterone, skin irritation or transfer concerns with gels, and minor extrusion or skin reactions with pellets.
Hematologic: Erythrocytosis
The most common laboratory abnormality during TRT is erythrocytosis — elevation of hematocrit above the normal range, sometimes well above. Testosterone stimulates erythropoiesis directly and through the bone marrow erythropoietin axis. The Endocrine Society 2018 Guideline recommends action when hematocrit exceeds 54%: dose reduction, switching to a more stable delivery method (gel or weekly subcutaneous), or therapeutic phlebotomy.
The clinical significance of mild erythrocytosis remains debated, but extreme elevations are associated with increased blood viscosity and theoretical thrombotic risk. Hematocrit checks are part of standard monitoring at 3 months, 6 months, and annually. Injection therapy produces higher hematocrit elevations than gels in head-to-head studies.
Cardiovascular Considerations
The TRAVERSE trial — published in the New England Journal of Medicine in 2023 — randomized over 5,200 hypogonadal men with high cardiovascular risk to TRT or placebo for an average follow-up of 22 months. The primary outcome (composite of cardiovascular death, nonfatal MI, or nonfatal stroke) was non-inferior in the TRT arm. This represents the strongest evidence to date that, at appropriate doses, TRT does not increase major cardiovascular events in hypogonadal men.
The trial did identify increased rates of atrial fibrillation, pulmonary embolism, and acute kidney injury. The FDA updated TRT labels in 2024 to reflect these specific risks while removing the prior broad cardiovascular warning. Men with a history of atrial fibrillation, recent venous thromboembolism, or severe cardiac disease should discuss timing and risk with their clinician before starting TRT.
When to seek emergency care: Call 911 or go to the nearest emergency room if you experience chest pain, severe shortness of breath, sudden one-sided weakness or speech difficulty, or a swollen and painful leg while on TRT — these can signal myocardial infarction, pulmonary embolism, stroke, or deep vein thrombosis.
Fertility Suppression
Exogenous testosterone suppresses pituitary LH and FSH, halting spermatogenesis in approximately 90% of men within 3 to 6 months of starting therapy. The result is azoospermia or severe oligospermia. This is reversible in most cases after stopping TRT, but recovery can take 6 to 24 months and is not guaranteed. Men trying to conceive should use fertility-preserving alternatives like clomiphene or hCG, or bank sperm before starting TRT. Reproductive urology evaluation is appropriate for men with current or future fertility plans.
Prostate Considerations
The historical concern that TRT causes or accelerates prostate cancer has not been borne out in modern trials. PSA elevations of 0.5 to 1 ng/mL are typical in the first year and stabilize thereafter. The Endocrine Society and AUA recommend a baseline PSA and DRE before initiation in men over 40, with PSA monitoring at 3 to 6 months and annually. Men with active prostate cancer are generally not TRT candidates; men with treated prostate cancer can sometimes be treated with TRT after individualized assessment by a urologist.
Lower urinary tract symptoms from BPH may worsen modestly on TRT, although this is inconsistent in trials. Men with severe baseline urinary symptoms warrant careful baseline assessment.
Gynecomastia and Estrogen Effects
Some testosterone is aromatized to estradiol, and a subset of men on TRT develop breast tenderness or visible gynecomastia. This is more common at higher doses and in men with higher body fat (more aromatase activity). Mild symptoms often resolve with dose reduction. Persistent gynecomastia is sometimes treated with selective estrogen receptor modulators (tamoxifen, raloxifene) or aromatase inhibitors, though the latter are off-label for this indication. See our gynecomastia guide for the broader picture and estrogen dominance in men for related discussion.
Sleep Apnea
TRT can worsen obstructive sleep apnea in susceptible men, possibly through both upper airway and central mechanisms. Men with untreated severe sleep apnea should generally have apnea treated before starting TRT, and new-onset snoring or daytime sleepiness on TRT warrants a sleep study.
Long-Term Risks Beyond Five Years
Long-term randomized data beyond 5 years remain limited. Observational cohorts and registry data suggest that, with appropriate monitoring, men maintained at physiologic levels do not show excess mortality compared to non-treated hypogonadal men. The biggest unknowns relate to extremely long-term (15 to 20 year) effects, which simply have not been formally studied. Annual monitoring and individualized risk assessment remain the standard.
Monitoring Schedule
The Endocrine Society guideline recommends checking serum testosterone, hematocrit, and PSA at 3 months, 6 months, and annually thereafter. Lipid panel is often included in baseline and follow-up labs. Symptom assessment, blood pressure, and weight checks accompany lab monitoring. Bone density (DEXA) every 1 to 2 years is reasonable in men with low baseline density. Men reporting new symptoms — chest pain, dyspnea, leg swelling, severe headache — should be evaluated promptly.
Who Should Not Use TRT
Absolute or relative contraindications include active untreated prostate cancer, active breast cancer (rare in men), erythrocytosis with hematocrit over 54%, untreated severe sleep apnea, severe lower urinary tract symptoms, recent (within 6 months) myocardial infarction or stroke, uncontrolled heart failure, untreated active venous thromboembolism, and current or planned attempts at conception. The AUA Guideline covers the full list. For broader context on related conditions, see the medical conditions hub, the low testosterone guide, and the TRT options guide.
Frequently Asked Questions
Does TRT cause hair loss?
It can. Testosterone is partially converted to dihydrotestosterone (DHT), the hormone driving male-pattern baldness. Men with genetic susceptibility may notice accelerated hair thinning. Concurrent finasteride suppresses DHT and is sometimes prescribed for this reason, though it carries its own sexual side effect profile.
Will TRT make my testicles smaller?
Yes. Suppression of LH and FSH leads to reduced testicular size in most men within months. This change reflects fertility suppression and is partially reversible after stopping TRT. Adding hCG to the regimen helps preserve testicular volume and intratesticular testosterone for men who want to maintain fertility or testicular size.
How dangerous is high hematocrit on TRT?
Mild elevation up to 52 to 54% is common and typically managed by dose adjustment or formulation switching. Hematocrit consistently over 54% is associated with increased blood viscosity and theoretical thrombotic risk; therapeutic phlebotomy or treatment pause is recommended. Monitoring catches the issue before it becomes dangerous.
Can I drink alcohol on TRT?
Modest alcohol use is generally compatible with TRT. Heavy drinking lowers endogenous testosterone (less relevant on replacement therapy) and increases aromatization to estradiol, which can worsen gynecomastia and water retention. Routine excessive drinking also damages the liver, complicating overall management.
The Bottom Line
TRT side effects are well characterized, monitorable, and mostly manageable with dose adjustment or formulation switching. The cardiovascular concerns that dominated discussions a decade ago have been substantially clarified by the TRAVERSE trial, replaced by a more nuanced risk profile (atrial fibrillation, pulmonary embolism). Men starting TRT with appropriate diagnosis, regular monitoring, and an experienced clinician can expect meaningful symptomatic benefit at acceptable risk. Men starting through unregulated channels without monitoring face significantly higher risk of complications.