Here’s another reason for men to be wary of taking testosterone, especially if it’s not medically indicated: It may increase the risk of rare but life-threatening blood clots, according to a 2019 study published online in JAMA Internal Medicine. For the study, researchers analyzed insurance records from 39,622 men (average age 57) who experienced a venous thromboembolism (VTE) between 2011 and 2017. A VTE occurs when a blood clot forms in a vein, usually a deep vein in the legs, and travels to the lungs, causing a pulmonary embolism.
Having used testosterone in the previous six months more than doubled the risk of developing a VTE, compared with not having taken testosterone within six months (though the overall risk of these clots is low to begin with). This was true regardless of how the testosterone was administered—gel, patch, or intramuscular injection.
It’s not clear how testosterone may raise the risk of clots, but one idea is that it increases the proportion of red blood cells in the blood, making the blood more viscous. Prescription testosterone has already been linked with a higher risk of heart attack and stroke, prompting the FDA to issue warnings about it in 2014 and 2015; yet sales of the therapy have remained relatively high.
If you are considering testosterone therapy, talk to your doctor and weigh the perceived benefits of therapy against the potential risks for your particular situation. Also, don’t overlook lifestyle interventions that may address some low-testosterone symptoms; for example, switching to a healthier diet, losing excess weight, incorporating a regular exercise routine into your day, and addressing any sleep or psychological issues you may have.