Hundreds of thousands of older people who take common drugs could be at increased risk of mental decline and death, research suggests.
A study of 13,000 people found risks from over-the-counter and prescription drugs, including some antihistamines, painkillers, blood thinners and eye drops for glaucoma.
Researchers say well-known side-effects of the drugs could have an impact on the brain, increasing the risk of decline and death.
They analysed over 80 drugs for “anticholinergic activity”, a potential side effect which affects the brain by blocking a key neurotransmitter called acetylcholine.
The drugs were ranked from one to three according to the strength of this activity, with drugs scoring one having a mild effect, two a moderate effect and three causing the most serious concern.
Taking a combination of drugs – such as four scored at one each – increased the risks, with experts saying the threshold for damage in patients was a total score of about four.
The risk was cumulative, based on the number of drugs taken and the strength of each drug’s effect.
Some of the most dangerous (score three) drugs are commonly available, including the antihistamines chlorphenamine (used in the brand Piriton) and promethazine (used in Phenergan), anti-depressants amitriptyline (used in several brands) and paroxetine (used in Seroxat) and the incontinence drug oxybutynin (used in Ditropan).
The blood thinner warfarin scored one as did heartburn drug ranitidine (used in the brand Zantac), alongside painkiller codeine and timolol maleate eye drops.
Led by experts at the University of East Anglia (UEA), the study involved people aged 65 and over from across the UK.
Of the group, 48 per cent were taking medicines with possible or definite anticholinergic properties, of which 508 (four per cent) were taking drugs with definite anti-cholinergic properties.
The results showed that one in five people taking drugs with a total score of four or more had died by the end of the two-year study, compared with only seven per cent of those taking no anti-cholinergic drugs. That represents around treble the risk.
For every additional point scored, the odds of dying increased by 26 per cent, the study also found.
Those people taking drugs with a combined score of five or more scored more than four per cent lower in a cognitive function test than those taking none of the drugs.
The study, published in the Journal of the American Geriatrics Society, forms part of the Medical Research Council’s Cognitive Function and Aging Studies project, which hopes to uncover risk factors for dementia.
It included experts from the University of Cambridge and Indiana University in the US.
Lead author Chris Fox, clinical senior lecturer at Norwich Medical School, UEA, said: “This is the first large-scale study into the long-term impact of medicines which block acetylcholine – a common brain neurotransmitter – on humans, and our results show a potentially serious effect on mortality.”