Commonly used drugs, including some antihistamines, painkillers, blood thinners and eye drops for glaucoma, have been linked to an increased risk of mental decline and death.
Researchers said well-known side-effects of the drugs could have an impact on the brain, putting hundreds of thousands of older people at risk, with those taking a combination of medications facing an increased threat.
A study of 13,000 people, published in the Journal of the American Geriatrics Society, analysed more than 80 drugs for “anticholinergic activity”, a potential side-effect that affects the brain by blocking a key neurotransmitter called acetylcholine.
The drugs were ranked 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. Experts say the threshold for damage in patients was a total score of about four.
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).