For men over 40 with low testosterone, taking testosterone therapy doesn't clearly raise the risk of stroke—but it also might raise it by up to half, so we can't say for sure it's safe.

For men who have both diabetes and low testosterone, taking testosterone therapy might lower their chance of having a stroke by about 12% over about three and a half years.

Giving testosterone to older men with low levels doesn’t seem to make their heart problems worse, but it also might slightly increase the risk — so we can’t say for sure if it’s completely safe for the heart.

For men over 40 with low testosterone, taking testosterone therapy doesn't clearly raise or lower the chance of a heart attack — but it might still increase it by up to 28%, so we can't say for sure it's safe.

Giving testosterone to older men with low levels doesn’t seem to make them more likely to die, but we can’t be totally sure it’s completely safe—there’s still a small chance it could be harmful.

Men between 55 and 67 who take testosterone therapy may be 13% less likely to die from heart disease than men who don’t take it, based on a long-term study tracking them for 18 years.