Deep vein thrombosis (DVT) occurs when a blood clot forms in a deep vein — usually in the leg. Pulmonary embolism (PE) occurs when that clot breaks free and travels to the lungs, where it can be life-threatening. Testosterone therapy raises risk of both conditions through a well-documented mechanism: TRT stimulates the bone marrow to produce more red blood cells (erythropoiesis), which thickens the blood (polycythemia) and dramatically increases clotting tendency.

The FDA's 2015 black box warning was specifically issued for VTE risk — not cardiovascular risk generally. This means that for DVT and PE plaintiffs, the regulatory foundation of the lawsuit is particularly strong: the FDA explicitly recognized and required warning about this exact injury. Men who developed DVT or PE while using any form of testosterone replacement therapy should contact an attorney to evaluate their claim, even if the condition was treated and resolved.