Paracetamol is one of the most widely used pain medicines in the world, but taking high prescription doses regularly may have an unexpected effect on blood pressure.
A study from the University of Edinburgh found that people with high blood pressure experienced a measurable rise after taking paracetamol every day for two weeks. The finding raises questions about its long-term use for chronic pain in people already at risk of heart disease.
Paracetamol, also called acetaminophen in countries such as the United States, is commonly used for headaches, fever, muscle pain and other painful conditions.
It has often been considered a safer choice than non-steroidal anti-inflammatory drugs, or NSAIDs, such as ibuprofen. NSAIDs can raise blood pressure and may increase cardiovascular risk in some people.
This difference has made paracetamol a common option for people who need ongoing pain relief but have heart or blood pressure concerns.
However, scientists have had limited evidence about what happens to blood pressure when people take large doses of paracetamol regularly rather than occasionally. The University of Edinburgh researchers set out to examine that question directly.
The study involved 110 adults who had a history of high blood pressure. Participants received either paracetamol or a placebo, which looked like the medicine but contained no active drug. The paracetamol dose was one gram four times a day, giving a total of four grams each day for two weeks.
Four grams per day is a high dose, but it has commonly been used as a standard maximum prescription dose for adults with chronic pain. The study was therefore designed to examine regular therapeutic use rather than an overdose. Researchers closely measured the participants’ blood pressure to see whether it changed during treatment.
The results showed that blood pressure increased while participants were taking paracetamol compared with the placebo treatment. The size of the rise was similar to increases previously seen with NSAIDs.
This was important because paracetamol has often been chosen specifically to avoid some of the cardiovascular concerns associated with those drugs.
High blood pressure places extra strain on arteries and the heart. Over many years, it can damage blood vessels and increase the risk of heart attack, stroke, kidney disease and other health problems. Even relatively small increases in average blood pressure across a population can therefore matter for long-term health.
Based on previous knowledge about the relationship between blood pressure and cardiovascular disease, the researchers estimated that an increase of the size seen in the trial could translate into roughly a 20% increase in the risk of heart disease or stroke if it were maintained over a long period.
This figure is an estimate rather than a direct finding that 20% more participants had heart attacks or strokes. The study lasted only weeks and was not designed to measure those long-term events.
Professor James Dear and colleagues said the results are particularly relevant to people who use paracetamol regularly for chronic pain.
Someone who takes a tablet occasionally for a headache or fever is in a very different situation from a person taking several grams every day for months or years. The study did not show that occasional paracetamol use causes the same blood pressure effect.
The researchers therefore suggested that doctors should think carefully when starting long-term paracetamol treatment in people with hypertension or other cardiovascular risks.
One approach may be to begin with the lowest useful dose and monitor blood pressure after treatment starts. Continuing need for the medicine can also be reviewed over time.
The findings do not mean that people prescribed paracetamol should suddenly stop taking it. Pain itself can seriously affect sleep, mobility and quality of life, and appropriate pain treatment remains important. Decisions about long-term medication should consider both the benefits of pain relief and possible risks for each individual.
For some people with ongoing pain, non-drug approaches may also form part of treatment. Depending on the cause of pain, these can include physical therapy, suitable exercise, weight management or other approaches recommended by healthcare professionals.
Other medicines may sometimes be considered, although they can have their own risks and side effects.
The study has several strengths. It directly compared paracetamol with a placebo and repeatedly measured blood pressure, making it more informative than simply observing people who happened to use the drug.
Because participants received both treatments as part of the research design, the scientists could more clearly examine whether paracetamol itself was connected with the change.
There are also important limitations. The trial included only 110 people and tested treatment for two weeks, so it cannot tell researchers exactly what happens after months or years of use. It also focused on people who already had high blood pressure, meaning the results may not apply in the same way to people with normal blood pressure.
The findings therefore do not show that paracetamol is generally unsafe. Instead, they suggest that regular high-dose use deserves more attention, particularly in people who already have cardiovascular risk factors.
Larger and longer studies could help determine whether the rise in blood pressure continues during prolonged treatment and whether it actually leads to more heart attacks or strokes.
The research was led by Iain MacIntyre and colleagues at the University of Edinburgh and was published in the American Heart Association journal Circulation. The study adds an important caution to the long-standing view of paracetamol as an automatically safer choice for people with cardiovascular concerns.
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