Blood-clot prevention on testosterone replacement therapy (TRT) is mainly about monitoring your complete blood count, preventing testosterone-induced erythrocytosis, and addressing other risks such as smoking, sleep apnea, obesity, and prolonged immobility. A hematocrit of 54% or higher requires medical review. Do not start aspirin or an anticoagulant only because you use TRT.

TRT Blood-Clot Prevention at a Glance

Prevention step What to do
Check hematocrit Get a CBC before TRT, again about 3 to 6 months after starting, and at least once a year after your levels are stable.
Act on a high hematocrit A hematocrit of 54% or higher usually requires a dose review, a temporary pause, or another medical intervention.
Review the TRT formulation Injectable testosterone is more likely than topical testosterone to raise hemoglobin and hematocrit.
Treat other risks Address smoking, untreated sleep-disordered breathing, lung disease, obesity, dehydration, and prolonged immobility with a clinician.
Stay mobile Walk regularly during travel and after illness, surgery, or hospitalization.
Know the symptoms One-sided leg swelling or pain needs prompt medical assessment. Sudden breathing difficulty or chest pain requires emergency care.

Why Can TRT Affect Blood-Clot Risk?

TRT can affect blood-clot risk because testosterone can stimulate red blood cell production. This may raise hemoglobin and hematocrit, a condition called erythrocytosis.

The Endocrine Society identifies a hematocrit above 54% as a treatment-related problem. Its guidance recommends withholding testosterone until the level returns to a safer range, then reassessing the cause and usually restarting at a lower dose.

The link between medically prescribed TRT and venous blood clots is still uncertain. Earlier systematic reviews did not find a statistically significant overall increase in venous thromboembolism. However, the evidence was low certainty and could not rule out a clinically important risk.

The large TRAVERSE cardiovascular-safety trial found no meaningful increase in major cardiovascular events overall, but pulmonary embolism occurred more often in the testosterone group. The Endocrine Society discussed this pulmonary embolism signal in a July 16, 2026 statement.

1. Check Your Hematocrit Before and During TRT

Ask for a complete blood count, including hemoglobin and hematocrit, before starting or continuing TRT.

A practical monitoring schedule is:

  • Before starting TRT
  • About 3 to 6 months after starting
  • At least once a year after your results are stable
  • After a major dose or formulation change, based on your prescriber's plan

The American Urological Association recommends checking hemoglobin and hematocrit before TRT and advises intervention when hematocrit reaches 54% or higher. The Endocrine Society also recommends baseline testing, follow-up after 3 to 6 months, annual testing, and withholding TRT if treatment-related erythrocytosis develops.

A high hematocrit does not prove that you have a blood clot. It tells your clinician to investigate and address a possible treatment-related risk.

2. Do Not Ignore a Rising Hematocrit

If your hematocrit rises while you are using TRT, your clinician may:

  1. Repeat the CBC to confirm the result.
  2. Review your testosterone dose and blood testosterone level.
  3. Reduce the dose or pause TRT.
  4. Check for smoking, sleep-disordered breathing, lung disease, high altitude, and other causes of erythrocytosis.
  5. Consider changing from an injectable formulation to a topical option when appropriate.
  6. Consider therapeutic phlebotomy in selected cases.

Do not change your dose or arrange repeated blood donations without medical guidance. Phlebotomy can lower hematocrit, but it does not address excessive testosterone dosing or an untreated underlying condition.

3. Ask Whether Your TRT Formulation Is Contributing

Injectable testosterone, especially intramuscular testosterone, tends to produce larger testosterone peaks. It is also more likely to raise hemoglobin and hematocrit than transdermal gel or other topical formulations.

The Endocrine Society reports less erythrocytosis with transdermal testosterone than with injectable testosterone. The AUA identifies injectable testosterone as producing the largest treatment-related increases in hemoglobin and hematocrit.

If your hematocrit rises more than once, ask whether a lower dose, a different injection schedule, or a non-injectable formulation would be appropriate. The right option depends on your diagnosis, testosterone levels, symptoms, treatment goals, and other health conditions.

4. Treat Other Blood-Clot Risks

TRT is only one part of your overall risk. Discuss these factors before starting TRT or if your hematocrit rises:

  • A previous deep-vein thrombosis or pulmonary embolism
  • A family history of unusual or recurrent blood clots
  • Known thrombophilia or another clotting disorder
  • Smoking or nicotine use
  • Obesity and prolonged inactivity
  • Recent surgery, injury, hospitalization, or long-distance travel
  • Cancer
  • Untreated sleep-disordered breathing
  • Chronic lung or heart disease

The European Academy of Andrology recommends reviewing personal and family histories of venous thromboembolism, along with other clot risks, before starting testosterone. Smoking and pre-existing respiratory conditions may also increase the likelihood of TRT-related erythrocytosis.

5. Prevent Clots During Long Periods of Sitting

For flights, road trips, desk work, or other periods lasting several hours:

  • Stand up and walk around every 1 to 2 hours when possible.
  • Flex and extend your ankles and knees while seated.
  • Avoid restrictive clothing.
  • Resume normal movement as soon as possible after illness, surgery, or hospitalization.
  • Ask a clinician whether compression stockings or preventive medication are appropriate if you have other clot risks.

The Centers for Disease Control and Prevention recommends movement during prolonged travel. It also advises that preventive medication should depend on your individual risk rather than be used automatically.

Should You Take Aspirin to Prevent TRT Blood Clots?

Usually, no. Do not start aspirin or an anticoagulant without a clinician's recommendation.

Aspirin and anticoagulants reduce clotting, but they can also cause serious bleeding. They are used for specific cardiovascular or clotting indications, not just because someone uses testosterone.

If your hematocrit is high, correcting the TRT-related problem and investigating the cause is more appropriate than taking a blood thinner on your own.

When to Seek Urgent Medical Care

Possible symptoms of a deep-vein thrombosis include:

  • New swelling in one leg or arm
  • Unexplained pain or tenderness
  • Warmth
  • Red or discolored skin

Contact a healthcare professional promptly if these symptoms develop.

Possible symptoms of a pulmonary embolism include:

  • Sudden or unexplained shortness of breath
  • Chest pain, especially pain that worsens with deep breathing or coughing
  • Coughing up blood
  • A rapid or irregular heartbeat
  • Lightheadedness, fainting, or collapse

These symptoms require immediate emergency medical attention. Do not wait for a routine TRT appointment.

Bottom Line

To reduce blood-clot risk on TRT, monitor your hematocrit, keep your testosterone dose within the prescribed range, investigate results near or above 54%, address smoking and sleep-related breathing problems, stay mobile, and learn the symptoms of DVT and pulmonary embolism.

The evidence does not show that TRT causes blood clots in everyone. However, a rising hematocrit and the pulmonary embolism signal seen in TRAVERSE make regular medical follow-up important.