Experts analyzed data on more than 30,000 Swedish men being treated with hormone therapy for prostate cancer. They found that these men had a slightly higher risk of blood clots.
Men without prostate cancer had about a 1 in 1,000 chance of getting a blood clot. For those on the hormones that risk increases to about 4 in 1,000.
Researchers aren't sure why hormone therapy may be linked to clots but suspect it is connected to testosterone.
Hormone treatment is given to men with advance prostate cancer and there are no real alternatives.
There is more on this research in the British Medical Journal.