Blood pressure pills taken by millions worldwide could raise the risk of lung cancer, research has found.
It showed that patients on ACE inhibitors were 14 per cent more likely to develop the cancer than those on other types of drugs.
The risk went up the longer patients were on the medication. Those taking them for five years were 22 per cent more likely to get lung cancer rising to 31 per cent if they were on them for ten years.
Scientists believe the drugs cause the accumulation of chemicals called bradykinin on the lung which in turn leads to cancer.
But other experts cast doubt on the findings and pointed out that the lung cancer could simply be caused by patients smoking at the same time as taking the drugs.
Up to five million patients in the UK are prescribed ACE inhibitors and they usually taken for high blood pressure or following a heart attacks.
The most common ACE inhibitor, ramipril, was prescribed more than 27 million times in England in 2017, costing £41 million, according to the NHS.
It is branded as Tritace in the UK but marketed as Altace in the US, where figures show there are around 163million prescriptions for ACE inhibitors each year.
Other common names for the drugs include captopril, cilazapril and enalapri.
They work by reducing the activity of the angiotensin-converting enzyme, or ACE for short. By blocking this enzyme, the blood vessels relax and widen and blood pressure is lowered.
An estimated 103 million adults in the US, which is almost half the adult population, have high blood pressure, according to statistics this year from the American Heart Association.
The study, published in the BMJ, looked at 992,000 adults who were prescribed blood pressure drugs in the UK between 1995 and 2015.
Patients were taking one of two types of pills either ACE inhibitors or angiotensin receptor blockers, which work in a different way.
Compared to patients on the angiotensin receptor blockers, those on ACE inhibitors were 14 per cent more likely to be diagnosed with lung cancer over a six-year period.
The study was carried out by researchers at McGill University in Montreal, Quebec, in Canada, who called for ‘additional studies, with long term follow-up, to investigate the effects of these drugs on incidence of lung cancer’.
They said that although a 14 per cent increased risk might not seem very much, ‘small relative effects could translate into large absolute numbers of patients at risk for lung cancer’.
The researchers added: ‘Given the potential impact of our findings, they need to be replicated in other settings, particularly among patients exposed for longer durations.’
But Professor Stephen Evans, an expert on the effects of drugs at the London School of Hygiene and Tropical Medicine, said it was unlikely that the drugs were causing lung cancer.
‘Drawing strong conclusions and talking about public health impact in this situation seems premature,’ he said.