Do steroids cause blood clots? The answer depends on which type of steroid is involved, but research links both main types to an increased risk. Corticosteroids, such as prednisone, are associated with a higher risk of clots in the veins. Anabolic-androgenic steroids (AAS), the testosterone-related compounds used in bodybuilding, are associated with changes in the blood that can promote clotting, and with clot-related events such as heart attacks and strokes in young users.
This article explains the evidence for each type of steroid separately, how they may affect clotting, and the warning signs of a blood clot that require urgent medical attention.
Two types of steroids, two different questions
“Steroids” can refer to two very different classes of medication. Corticosteroids are anti-inflammatory medicines used for conditions such as asthma, arthritis, and inflammatory bowel disease. Anabolic-androgenic steroids are related to testosterone and are used medically for low testosterone, and non-medically to build muscle. Our guide to the key facts about steroids explains the difference in more detail.
Because they act on different receptors and have different effects, their links to blood clots are studied separately.
Venous and arterial clots
Blood clots can form in veins or in arteries, with different consequences. Clots in the veins usually form in the legs, a condition called deep vein thrombosis (DVT), and can travel to the lungs, causing a pulmonary embolism. Clots in the arteries can block blood flow to the heart or brain, causing a heart attack or stroke. Together, DVT and pulmonary embolism are called venous thromboembolism (VTE).
Do corticosteroids increase the risk of blood clots?
Yes. Large population studies have found that people currently taking corticosteroids by mouth have a higher risk of VTE than people who are not. In a nationwide Danish study, current use of corticosteroids taken by mouth was associated with roughly double the risk of VTE, with the highest risk among people who had just started treatment and among those taking higher doses (Johannesdottir et al., 2013).
Even short courses are associated with increased risk. A large US study found that adults prescribed oral corticosteroids for less than 30 days had a higher rate of VTE in the following month than in the period before treatment (Waljee et al., 2017).
Part of this association may reflect the illnesses being treated, since inflammation itself increases clotting risk. Even so, the evidence suggests corticosteroids contribute independently.
Should you stop taking prescribed corticosteroids?
No, not without speaking to your doctor. Corticosteroids are important treatments for many conditions, and for most people the benefits outweigh the clotting risk. Stopping them suddenly after longer use can also be dangerous, because the body’s own production of the related hormone, cortisol, may be suppressed. Anyone concerned about their clotting risk should discuss it with their prescriber.
Do anabolic steroids increase the risk of blood clots?
The evidence suggests they can. Anabolic steroid use has been associated with case reports and case series of DVT, pulmonary embolism, heart attacks, and strokes, including in young people without other obvious risk factors. Reviews of the evidence have identified several changes in the blood that may increase clotting risk (Chang et al., 2018).
Because most of this evidence comes from case reports and observational studies, it is not possible to say precisely how much AAS use increases clotting risk, or how this varies with compound, dose, and duration of use.
How might anabolic steroids promote clotting?
More red blood cells
Androgens stimulate the production of red blood cells. AAS use commonly raises hematocrit, the proportion of the blood made up of red blood cells, and in a prospective study of men using AAS, this rise was among the most consistent changes observed (Smit et al., 2022). A very high hematocrit, known as erythrocytosis, makes the blood thicker, which may increase the risk of clots.
Changes in platelets and clotting factors
AAS use has been associated with increased platelet activity and with changes in the proteins that form and break down clots. The overall effect of these changes is complex, and some findings point in different directions, but several studies suggest a shift toward a greater tendency to clot (Chang et al., 2018).
Effects on blood vessels and other risk factors
AAS use is also associated with raised blood pressure, unfavorable changes in cholesterol, and changes in the structure and function of the heart and arteries, all of which can contribute to clots in the arteries. Our articles on steroids and heart health and steroids and blood pressure explain these effects.
What about medical testosterone?
In 2014, the US Food and Drug Administration (FDA) required testosterone products to carry a general warning about the risk of VTE, based on reports of clots in men using testosterone. In the TRAVERSE trial, which studied testosterone replacement in men with low testosterone and elevated heart risk, pulmonary embolism occurred more often in the testosterone group than in the placebo group, although the numbers were small (Lincoff et al., 2023).
These findings apply to medically supervised replacement doses. Non-medical AAS use typically involves much higher doses, often of several compounds at once.
What increases clotting risk further?
The risk of a blood clot depends on many factors, and steroid use can add to others, including:
Recent surgery, injury, or long periods of immobility, such as long flights or bed rest.
A previous blood clot or a family history of clots.
Smoking, obesity, and cancer.
Estrogen-containing medications, such as some contraceptives, and pregnancy.
Dehydration, which can make the blood more concentrated.
Warning signs of a blood clot
Blood clots can be life-threatening, and early treatment makes a significant difference. Seek medical attention for:
Signs of DVT: swelling, pain, tenderness, warmth, or redness in one leg or arm, especially if one side is affected more than the other.
Signs of pulmonary embolism: sudden shortness of breath, chest pain that may worsen when breathing in, a rapid heartbeat, or coughing up blood.
Signs of a heart attack: chest pain or pressure, pain spreading to the arm, jaw, or back, sweating, nausea, or shortness of breath.
Signs of a stroke: sudden weakness or drooping on one side of the face or body, difficulty speaking, confusion, or loss of vision.
Signs of a pulmonary embolism, heart attack, or stroke are emergencies and require calling emergency services immediately. Blood clots are diagnosed with tests such as ultrasound, blood tests, and imaging, and treated by doctors, usually with anticoagulant medication. Telling a doctor about any steroid use, medical or non-medical, helps them assess the risk accurately.
The bottom line
Do steroids cause blood clots? Both main types of steroids are linked to increased clotting risk, in different ways. Corticosteroids taken by mouth are associated with a higher risk of clots in the veins, even with short courses, although for most people the benefits of prescribed treatment outweigh this risk.
Anabolic steroids are associated with increased red blood cell counts, changes in platelets and clotting proteins, and clot-related events such as DVT, heart attack, and stroke, although the size of the risk is uncertain. Knowing the warning signs of a blood clot, and seeking help quickly, matters for anyone using either type of steroid.
References
Chang S, Münster AB, Gram J, Sidelmann JJ. Anabolic androgenic steroid abuse: the effects on thrombosis risk, coagulation, and fibrinolysis. Seminars in Thrombosis and Hemostasis. 2018;44(8):734–746.
Johannesdottir SA, Horváth-Puhó E, Dekkers OM, et al. Use of glucocorticoids and risk of venous thromboembolism: a nationwide population-based case-control study. JAMA Internal Medicine. 2013;173(9):743–752.
Lincoff AM, Bhasin S, Flevaris P, et al. Cardiovascular safety of testosterone-replacement therapy. New England Journal of Medicine. 2023;389(2):107–117.
Smit DL, et al. Prospective study on blood pressure, lipid metabolism and erythrocytosis during and after androgen abuse. Andrologia. 2022;54(4):e14372. doi:10.1111/and.14372. Waljee AK, Rogers MAM, Lin P, et al. Short term use of oral corticosteroids and related harms among adults in the United States: population based cohort study. BMJ. 2017;357:j1415.
