Men with factor V Leiden can still receive testosterone therapy

have Factor V Leiden, but I have been wanting to do testosterone replacement therapy. I have heard that testosterone causes blood clots. Obviously, with FVL, that would be a huge deal for me. Is this true? Does it cause clots? Or is it safe for me to do?

DEAR READER >> Factor V Leiden is a common genetic variant that increases a person’s risk for developing a blood clot. However, a person who has never had a blood clot, but who is identified as heterozygous (meaning they only have one copy of the gene, which is by far the more common scenario) for factor V Leiden is still not likely to have a blood clot during their lifetime, and is not recommended for treatment to prevent a blood clot.

Testosterone replacement therapy in men with FVL does increase the risk of blood clots in some studies, but not in others. In the studies that have shown an increase in risk, the risk has been estimated as approximately one person per thousand treated with testosterone each year.

However, the risk occurs mostly during the first three months, and after two years on treatment, there is no additional risk.

Thus, roughly one man per 500 who has FVL and gets treated with testosterone will get a clot, according to the studies that show an increase in risk.

This is a small risk, but a blood clot is a significant potential problem. So the risk of getting a clot should certainly go into the discussion about whether to give testosterone replacement to a man with FVL and symptomatic low testosterone levels.

Most of the men I have seen with this issue have elected to take the replacement.