Doctors should be cautious when prescribing the painkiller, researchers said, and start patients on as low a dose as possible.
Paracetamol, which is commonly prescribed on a regimen of one gram four times a day for chronic pain, has been considered a “safer” alternative to other painkillers due to its reduced side effects.
But authors of the study, funded by the British Heart Foundation and published in scientific journal Circulation, found regular use increased blood pressure in those who already had a history of hypertension.
High blood pressure is known to increase the risk of heart attack and stroke.
Around one in ten people in Scotland are thought to have a prescription for one gram of paracetamol four times daily, while more may be purchasing this dosage over the counter.
About one in three adults are believed to have high blood pressure. Older people are most at risk of having both high blood pressure and taking regular paracetamol – the combination that may lead to an increased risk of heart attack and stroke.
In the study, 103 Scottish adults with a history of high blood pressure were given one gram of paracetamol four times a day or placebo, for two weeks.
All patients received both treatments, with the order randomised and blinded.
Those prescribed paracetamol saw a significant increase in their blood pressure compared to those taking the placebo.
This rise was similar to that seen with non-steroidal anti-inflammatory drugs such as ibuprofen, despite paracetamol being seen as a safer option. It could be expected to increase the risk of heart disease or stroke by around 20 per cent, experts said.
Researchers said doctors prescribing regular paracetamol should consider whether a lower dose would be as effective.
However, they added that if a patient needs paracetamol to cope with chronic pain, this should not necessarily be avoided.
The study authors also stressed the results did not refer to occasional low-dose use of paracetamol.
Lead Investigator Dr Iain MacIntyre, consultant in clinical pharmacology and nephrology at NHS Lothian, said: “This is not about short-term use of paracetamol for headaches or fever, which is, of course, fine. But it does indicate a newly discovered risk for people who take it regularly over the longer term, usually for chronic pain.”
Professor James Dear, personal chair of clinical pharmacology at Edinburgh University, said: “This study clearly shows that paracetamol – the world’s most used drug – increases blood pressure, one of the most important risk factors for heart attacks and strokes. Doctors and patients together should consider the risks versus the benefits of long-term paracetamol prescription, especially in patients at risk of cardiovascular disease.”
Principal investigator Professor David Webb, chair of therapeutics and clinical pharmacology at Edinburgh University, said: “Given the substantial rises in blood pressure seen in some of our patients, there may be a benefit for clinicians to keep a closer eye on blood pressure in people with high blood pressure who newly start paracetamol for chronic pain.”