LONDON — Regularly taking some of the most popular painkillers on the market is linked to a much greater risk of stroke and heart attack from higher blood pressure, according to American research published yesterday.

Participants in a large American study who took paracetamol, aspirin, or nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, six or seven days a week over a two-year period were between a quarter to a third more likely to be diagnosed with highblood pressure.

Those who took 15 pills a week, regardless of type, have almost a 50% risk of higher blood pressure than those who do not.

More than 5 million Britons with osteoarthritis, migraines, or back pain either buy the drugs over the counter regularly or are prescribed them, though dosages differ.

Those diagnosed with hypertension — high-blood pressure — are at greater risk of stroke, heart attack, heart disease, and kidney failure.

The findings could pose a dilemma for some arthritis sufferers who have been told to switch to over-the-counter painkillers because of fears of heart problems linked to some prescription drugs.

Graham MacGregor, the professor of cardiovascular medicine at St. George’s Hospital, London, and chairman of the Blood Pressure Association, said: “High blood pressure is the biggest cause of death and disability in Britain.

“Even though the increased risks are small in this study, they are important. If you take a couple of paracetamol for a headache, that’s fine, but patients need to be aware if they are on long-term painkillers they need to get their blood pressure checked.”

Researchers led by Dr. John Forman of Harvard Medical School studied 16,000 male volunteers in a long-term research project.

They were asked about their use of paracetamol, aspirin, and NSAIDs, and whether they had had a diagnosis of high-blood pressure in the preceding two years.

Those taking paracetamol, aspirin, or NSAIDs six or seven days a week were respectively 34%, 38% and 26% more likely to have been diagnosed with it than those who had not been taking painkillers regularly.

Compared with men who took no pain relief medication, participants who took 15 or more pills each week, irrespective of type, had a 48% higher risk of higher blood pressure.

Writing in the Archives of Internal Medicine, the journal of the American Medical Association, the authors said: “These data add further support to the hypothesis that nonnarcotic analgesics independently elevate the risk of hypertension.

“Given their common consumption and the high prevalence of hypertension, our results may have substantial public health implications and suggest that these agents be used with greater caution.”

The researchers said the link with increased blood pressure may be caused by all three painkillers inhibiting the effect of vasodilatory prostaglandins — chemicals that relax the blood vessels.

They also believe paracetamol, the world’s most widely used painkiller, could promote the accumulation of volatile chemicals called free radicals or impair the functioning of blood vessel lining.

Around 16 million people in Britain have high-blood pressure. It rarely has symptoms and is usually only discovered on a visit to the doctor.

Doctors and patient groups stressed that patients should not change their medication without taking medical advice.

Ellen Mason of the British Heart Foundation said: “We advise that painkillers should be taken at the lowest possible dose for the shortest amount of time. All medicines have side effects, and if you find yourself in frequent need of pain relief, it makes good sense to discuss your health with a pharmacist or GP. If you take prescribed painkillers regularly for conditions such as arthritis, which can cause chronic debilitating pain, the relief from symptoms may well outweigh the health risks.”

Alan Silman of the Arthritis Research Campaign said: ” We should be careful about interpreting these results. We don’t know whether people have a greater risk of high blood pressure because they are taking painkillers or because of the condition they are taking them for.

“Also we should remember high blood pressure has no symptoms. If someone is taking paracetamol regularly it is likely they go to their doctor more often. It is standard to take patients’ blood pressure, and so this could be explained by doctors being more likely to pick up their condition.”

Previous American research found women who regularly took paracetamol, NSAIDs, or aspirin had increased risks of high-blood pressure of 20%, 35% and 21%.

Vioxx, one of the NSAIDs, was taken off the market in 2004 after it was shown those who used it for 18 months or more were at increased risk of heart attacks and strokes.

Dr. Geoffrey Brandon of the Paracetamol Information Center, which receives funding from the pharmaceutical industry, said: “As with previous reports, this study reports a statistical association between analgesic use and hypertension but fails to show a causal relationship.

“We do not believe there is any evidence to warrant a recommendation for any change in use of paracetamol.”