Testosterone is a hormone that plays a significant role in various bodily functions, particularly in men, affecting muscle mass, bone density, and red blood cell production. Blood clots are gel-like clumps of blood that can form in veins or arteries, potentially leading to serious health issues like deep vein thrombosis (DVT) or pulmonary embolism (PE) if they obstruct blood flow. The question of whether testosterone can contribute to the formation of these clots is a common concern, especially for individuals considering or undergoing testosterone therapy. This article explores the scientific understanding of this potential link.
The Relationship Between Testosterone and Blood Clots
The connection between testosterone replacement therapy (TRT) and the risk of blood clots, specifically venous thromboembolism (VTE), has been a subject of extensive research and varying conclusions. Many studies, particularly randomized controlled trials (RCTs), have suggested that TRT is not associated with an increased VTE risk. For instance, a meta-analysis of 13 RCTs involving over 5,000 men found no statistically significant association between testosterone therapy and VTE compared to placebo. More recent analyses, including a 2024 meta-analysis of 14 RCTs, also concluded that TRT did not influence the risk of VTE.
However, some observational studies present conflicting evidence, indicating a potential transient increase in VTE risk. This risk appears especially during the initial months of testosterone treatment. For instance, one large study found starting testosterone treatment was associated with an increased VTE risk that peaked within the first six months, showing a 63% increased chance of a clot, translating to about 10 additional VTE cases per 10,000 person-years. This transient nature might explain some contradictory findings, though the overall evidence remains of low certainty and suggests a relatively small absolute risk increase.
The U.S. Food and Drug Administration (FDA) previously warned about a possible increased cardiovascular risk, including blood clots, with testosterone use. However, an update in February 2025, prompted by the TRAVERSE trial, led the FDA to remove language related to increased risk of major adverse cardiovascular events from testosterone product labeling. The TRAVERSE trial, which included over 5,200 men with low testosterone and existing cardiovascular risk, found no increase in cardiovascular events like heart attacks or strokes among treated men compared to placebo. While this trial focused on major adverse cardiovascular events and not solely VTE, it contributes to the understanding of testosterone’s overall cardiovascular safety.
How Testosterone May Influence Clot Formation
The main mechanism through which testosterone therapy can influence blood clot formation is by increasing red blood cell count, a condition known as polycythemia or erythrocytosis. Testosterone stimulates erythropoiesis, the production of red blood cells in the bone marrow. When red blood cell levels become high, the blood can thicken, increasing its viscosity. This thicker blood flows less easily through vessels, increasing the potential for clot formation.
Polycythemia is a side effect of testosterone therapy and a risk factor for thrombotic events like DVT, PE, stroke, and heart attack. Erythrocytosis is common in individuals receiving testosterone, especially with higher doses or injections. Monitoring red blood cell count, specifically hematocrit levels, is therefore a necessary part of managing testosterone therapy. While polycythemia is the main mechanism, researchers also consider other potential influences like testosterone’s effects on coagulation factors or platelet function, though these are less consistently linked to direct clot formation from TRT.
Identifying and Managing Clot Risk
Identifying and managing blood clot risk is a necessary aspect of testosterone therapy. Before starting treatment, a medical evaluation is necessary to assess overall health and identify any risk factors for blood clots. These factors can include a personal or family history of blood clots, genetic predispositions, cardiovascular conditions, or conditions that increase blood viscosity. Age, higher testosterone doses, and administration methods like injections might also influence risk.
Ongoing monitoring is a necessary part of risk management during testosterone therapy. Regular blood tests to check hematocrit levels are standard practice, performed before treatment and periodically thereafter. If hematocrit levels rise, indicating polycythemia, healthcare providers may adjust the testosterone dose or temporarily stop treatment. In some cases, therapeutic phlebotomy may be recommended to reduce the red blood cell count and lower the risk of clots. Open communication with a healthcare provider allows for personalized risk assessment and the implementation of strategies to mitigate complications.
Recognizing Blood Clot Symptoms
Recognizing blood clot symptoms is necessary for prompt medical attention. Symptoms vary depending on where the clot forms. For deep vein thrombosis (DVT), which occurs in a leg or arm, signs include swelling in the affected limb, pain or tenderness, and redness or discoloration of the skin. The skin in the affected area might also feel warm to the touch.
A pulmonary embolism (PE) occurs when a blood clot travels to the lungs, and its symptoms can be severe and sudden. These may include sudden shortness of breath, chest pain that worsens with deep breathing or coughing, a rapid heart rate, and unexplained coughing, sometimes with bloody mucus. If any of these symptoms appear, seek immediate medical attention. Early diagnosis and treatment prevent serious complications from blood clots.