The short answer
Since June 2014, every testosterone product sold in the United States has carried a general warning about blood clots in the veins. The warning covers deep vein thrombosis, a clot usually in the leg, and pulmonary embolism, a clot that travels to the lungs. It came from reports of these clots in men using testosterone, and it applies whether the testosterone is an injection, gel, capsule or pellet.
That warning is often confused with a different, better-known issue: testosterone raises red blood cell production, which is why hematocrit is checked on treatment. The two concerns overlap but are not the same, and understanding the difference tells you what to watch for and what to tell your provider before you start.
What the 2014 warning says
According to a 2016 study in the BMJ, the U.S. Food and Drug Administration and Health Canada both required, in June 2014, a new general warning about venous thromboembolism in the product information of all approved testosterone products.
Today that language appears in the warnings section of each label. The Depo-Testosterone label, for example, states that there have been postmarketing reports of venous thromboembolic events, including deep vein thrombosis and pulmonary embolism, in patients using testosterone products. It tells clinicians to evaluate leg pain, swelling, warmth and redness for a clot, to evaluate sudden shortness of breath for a lung clot, and to stop testosterone if a clot is suspected while it is worked up.
“Postmarketing reports” means the warning grew from cases reported after the products were on the market rather than from a trial designed to measure clot risk. That is why later studies matter for understanding how large the risk actually is.
How big is the risk, and when?
One widely cited estimate comes from that same 2016 BMJ study, a case-control analysis of more than 2.2 million men in UK primary care. Current testosterone use overall was not clearly linked to clots. But in the first six months of treatment, the rate of venous clots was about 1.6 times higher than in non-users, corresponding to roughly 10 extra clots per 10,000 men per year above a baseline of about 16. After six months, the extra risk was no longer seen.
The large TRAVERSE trial, which randomized 5,246 men with low testosterone and heart risk to testosterone gel or placebo, found no increase in heart attacks, strokes or cardiovascular deaths. But its published results reported a higher incidence of pulmonary embolism in the testosterone group, along with more atrial fibrillation and acute kidney injury. Our article on the TRAVERSE trial explains its findings in full.
| Source | What it found about clots |
|---|---|
| 2014 FDA label warning | Postmarketing reports of DVT and pulmonary embolism with testosterone products |
| BMJ case-control study (2016) | Higher clot rate in the first six months of treatment, not after |
| TRAVERSE trial (2023) | More pulmonary embolism with testosterone than placebo |
How this differs from the red blood cell concern
Testosterone stimulates the bone marrow to make more red blood cells. When the share of blood made up of red cells, the hematocrit, rises too far, blood becomes thicker. The Kyzatrex label explains that an increase in red blood cell mass may increase the risk of thromboembolic events, asks for hematocrit to be checked before starting and about every three months on treatment, and says to stop if it becomes elevated until it falls.
So the two concerns connect, but they work differently in practice:
| Red blood cell concern | Venous clot warning | |
|---|---|---|
| What it is | Testosterone raises hematocrit | Reports of DVT and pulmonary embolism in men on testosterone |
| How it is tracked | Regular blood tests | Your history before starting, and symptoms during treatment |
| What you can see coming | A rising number on your labs | Often nothing until symptoms appear |
| Main response | Dose change, pause or other steps based on labs | Urgent evaluation if symptoms appear; stop testosterone if a clot is suspected |
The key point: a normal hematocrit does not cancel the clot warning. Our pages on high hematocrit on TRT and the hematocrit blood test cover the lab side.
Which history to raise before starting
Your personal and family history is the most useful screening tool for clot risk, so bring it to the first visit. The Endocrine Society guideline lists thrombophilia, an inherited or acquired tendency to clot, among the conditions in which it recommends against starting testosterone.
Tell your provider about:
- Any past DVT or pulmonary embolism, even one with an obvious trigger such as surgery
- A known clotting disorder, such as factor V Leiden, which MedlinePlus Genetics describes as the most common inherited form of thrombophilia, carried in one copy by 3% to 8% of people of European ancestry
- Parents, siblings or children who had clots, especially at a young age or without a clear cause
- Recent surgery, injury, cancer or long periods of immobility
- Long-haul travel or desk-bound days, since sitting still for a long time raises DVT risk
- Smoking and obesity, which MedlinePlus lists among factors that add to clot risk in people with factor V Leiden
A family history does not automatically rule out testosterone, but it can change the plan: testing for an inherited clotting disorder, choosing a form and dose more carefully, or deciding against treatment. Our page for men with a history of blood clots goes deeper.
Symptoms that need urgent attention
Call 911 or go to an emergency room for sudden shortness of breath, chest pain that worsens with breathing, coughing up blood, or fainting. These can signal a pulmonary embolism.
Get same-day medical care for pain, swelling, warmth or redness in one leg, especially the calf. Tell whoever sees you that you take testosterone. Our page on blood clot warning signs on TRT lists what to watch for.
How Ultimate Male screens for clot risk
At our San Gabriel and Downey clinics, testosterone therapy starts with labs, including a complete blood count with hematocrit, and a one-on-one consultation with a PA-C or MD that covers your personal and family clotting history. If something in that history raises concern, the provider may suggest further testing or coordination with your primary care doctor or a hematologist before any decision.
On treatment, follow-up visits and labs keep an eye on hematocrit, and you leave with clear guidance on which symptoms mean calling the clinic and which mean calling 911. The first visit is an evaluation; it does not commit you or the provider to treatment. Book the free 10-minute phone call at 626-319-5261 to begin.
