Observational studies have suggested that paracetamol may raise BP; however, clinical trials are lacking.
The double-blind PATH-BP study included 110 individuals with hypertension who were randomised to receive paracetamol (1g four times daily) or matched placebo for two weeks. The participants then entered a two-week washout period before crossing over to the alternate treatment.
The researchers recorded participants' 24-hour ambulatory BP at the start and finish of each treatment period and compared the change in mean daytime systolic BP from baseline to end of treatment for the two study arms (primary outcome measure).
Observed BP increases
Results from the 103 patients who completed both arms of the study showed that paracetamol was associated with a significant increase in mean daytime systolic BP compared with placebo (132.8±10.5 to 136.5±10.1 mmHg versus 133.9±10.3 to 132.5±9.9 mmHg, respectively [p<0.0001]), with a placebo-corrected increase of 4.7mmHg (95% CI 2.9-6.6).
A significant increase in mean daytime diastolic BP was also observed for paracetamol compared with placebo (81.2±8.0 to 82.1±7.8 mmHg versus 81.7±7.9 to 80.9±7.8 mmHg, respectively [p=0.005]), with a placebo-corrected increase of 1.6mmHg (95% CI 0.5-2.7).
CV risk increased
The researchers conclude that regular daily intake of 4g paracetamol in individuals with hypertension increases systolic BP by approximately 5mmHg compared with placebo. They add that this increases CV risk and calls into question the safety of regular paracetamol use in this situation.
Commenting on the study findings, Dr Richard Francis, Head of Research at the Stroke Association, said: "This new and robust study adds to previous research and suggests regular paracetamol causes blood pressure to quickly increase in people who are already at risk of stroke and heart attacks. It's therefore important that doctors regularly review and weigh up the risks and benefits of prescribing paracetamol."
He added that further studies in people with normal healthy BP over longer time periods are needed to confirm the risks and benefits of using paracetamol more widely.
Also commenting on the study, Dr Dipender Gill, NIHR Clinical Lecturer in Clinical Pharmacology and Therapeutics at St George's, University of London, said that the findings highlight the importance of only taking paracetamol in cases where it is likely to offer meaningful benefit. He added: 'Further work is now required to more clearly establish the potential harms that may result from injudicious use of paracetamol.'