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Over-the-counter hay fever pills and sleeping tablets can increase the risk of Alzheimer’s, a study warned today.

The findings have “public health implications” about “potential safety risks”, according to scientists.

Other drugs for depression and bladder control were also linked to dementia .

The drugs have an ­“anticholinergic” effect, which blocks a chemical transmitter that people with Alzheimer’s lack.

Experts tracked the health of 3,434 over-65 and their use of anticholinergic drugs, like antihistamine diphenhydramine, for seven years.

During the study, 637 developed Alzheimer’s and 160 got other forms of dementia.

For people on high doses the risk of dementia was 54% higher compared to no use.

The report said: “These findings have public health implications for the health of older adults about potential safety risks because some anticholinergics are available as over-the-counter products.”

The findings, in journal Jama Internal Medicine, showed people were at higher risk if they took at least 10mg a day of antidepressant doxepin, 4mg a day of antihistamine diphenhydramine, or 5mg a day of oxybutynin for more than three years.

Dr Simon Ridley of Alzheimer’s Research UK, said: “This large study adds to some existing evidence linking anticholinergic drugs to a small increased risk of dementia, but the results don’t tell us that these drugs cause the condition.”