London - Men prescribed testosterone in middle age have a higher risk of suffering a heart attack or stroke, according to a study.
Testosterone has long been given to men with low levels of the hormone, but is increasingly being prescribed for symptoms of the "male menopause" such as fatigue and low libido.
A study of more than 15 000 British men has now found those taking testosterone are 21 percent more likely to have a heart attack, stroke or "mini-stroke".
The hormone regulates muscle mass and sex drive, and is thought to harden the arteries – potentially leading to blood clots, which cause strokes and heart problems.
Low testosterone rates have stayed stable over the last two decades. But replacement prescriptions have soared, raising concerns doctors are giving it out more readily.
The research, led by McGill University in Canada, found men aged 45 to 59 had the greatest increased risk of health problems if they took testosterone. The risk of a heart attack, stroke or transient ischaemic attack, also known as a ‘mini-stroke’, was highest in men within their first two years on the hormone.
Dr Christel Renoux, of McGill University, said: "There is limited evidence on the long-term clinical benefits of testosterone replacement therapy to effectively treat the modestly declining levels of endogenous testosterone levels of aging but healthy men.
"We strongly recommend that clinicians proceed with caution when considering prescribing testosterone replacement therapy and first discuss both the potential benefits and risks with patients." The study involved 15 401 men aged 45 and over with low testosterone – 850 of them suffered a heart attack, a stroke or a mini-stroke.
More than half of the men who were prescribed the testosterone top-up used a gel or cream, while a third had injections.
For those taking the hormone, the risk of cardiovascular events was a fifth higher compared to non-users. This works out as an extra 128 heart attacks, strokes or mini-strokes, meaning an extra three per 1 000 men who were prescribed the hormone.
The risk of these major health problems was 44 percent higher in men aged 45 to 59 and 35 percent higher for those in their first six months to two years of taking testosterone.
The study, published in the American Journal of Medicine, confirms fears voiced by many experts about the potential risks of the treatment. Dr Renoux added: "Further large and methodologically sound observational studies should be conducted to reaffirm these results."