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 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.

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.

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.

For men who have both diabetes and low testosterone, taking testosterone therapy might lower their chance of having a heart attack by about 15% over about three years.

For men over 40 with low testosterone, taking testosterone therapy might raise their risk of irregular heartbeats by more than half, which doctors should take seriously.