Does testosterone therapy have serious risks?

What the evidence says

Testosterone therapy does have some serious risks, even though a major study found it does not raise the overall chance of a heart attack or stroke the way doctors once feared.

The biggest trial on this, called TRAVERSE, followed over 5,000 men with heart disease or heart risk factors for an average of nearly two years. It found that testosterone gel was no worse than a placebo (fake treatment) for the combined risk of heart attack, stroke, or death from heart causes. But the testosterone group did have more cases of pulmonary embolism, which is a blood clot that travels to the lungs, more irregular heartbeat called atrial fibrillation, and more sudden kidney injury.

Testosterone can also thicken the blood by boosting red blood cell counts, a condition called polycythemia, which raises clot risk further. This is one reason doctors check blood counts regularly during treatment.

For the prostate, Canadian guidelines say testosterone should not be given to men with active, advanced prostate cancer, because there is strong evidence this could make the cancer grow. The link between testosterone and causing prostate cancer in men without it is less clear, but doctors still monitor prostate health closely during treatment.

Other risks include infertility, since testosterone can shut down the body's own sperm production, sometimes for a long time after stopping treatment. Testosterone therapy should only be started after checking hormone levels properly and discussing individual risks with a doctor, especially for anyone with existing heart disease, since Canadian and American guidelines both recommend caution in men whose heart disease is not stable.