Restoring testosterone can reduce rather than increase the risk of heart attacks and strokes in vulnerable older men, research has shown.
Scientists studied 755 heart patients aged between 58 and 78, some of whom were given supplements of the male hormone that was injected or administered in a gel.
Those who received the testosterone therapy were 80% less likely to suffer a cardiovascular event such as a heart attack or stroke than those who did not.
This was despite previous research suggesting that testosterone supplements can increase the risk of cardiovascular problems.
Last year the US Food and Drug Administration (FDA) required manufacturers of all approved testosterone products to add labels outlining the danger.
Lead researcher Dr Brent Muhlestein, from the Intermountain Medical Centre Heart Institute in Salt Lake City, US, said: "The study shows that using testosterone replacement therapy to increase testosterone to normal levels in androgen-deficient men doesn't increase their risk of a serious heart attack or stroke.
"That was the case even in the highest-risk men - those with known pre-existing heart disease."
A randomised clinical trial was now needed to clarify the picture, he said.
The study found that after one year, 64 patients who were not taking testosterone supplements suffered a major cardiovascular event. This compared with only 12 who were taking medium doses of testosterone, and nine who were receiving high doses.
The same trend was seen two years later, by which time 125 patients not treated with testosterone, 38 medium-dose patients and 22 high-dose patients had experienced a major event.
Dr Muhlestein added: "The FDA's warning was based on the best clinical information available at the time. As further information, like our research, becomes available - and especially after a large randomised clinical outcomes trial can be accomplished - hopefully the FDA will be able to change its warning."
The findings were presented at the American College of Cardiology's 65th annual scientific session in Chicago.