Commonly used drugs - for conditions such as heart disease, depression and allergies - have been linked to a greater risk of death and declining brain function by UK researchers.
They said half of people over 65 were prescribed these drugs.
The effect was greatest in patients taking multiple courses of medication, according to the study in the Journal of the American Geriatrics Society.
Dr Chris Fox, who lead the research at the University of East Anglia, said the relationship between the drugs was complex and that cause and effect had not been found.
"It is an association. We found that there is a link and it seems to be an increased risk," he said.
Dr Clare Gerada, who chairs the Royal College of GPs, cautioned that "every single medicine has a side effect and there is always a trade off".
Many of the drugs, she said, were prescribed for serious diseases where there was obviously a higher risk of death.
"We have to be mindful of the risks and benefits of anything we take," she said.
"Please don't all stop your medicines, because you could cause yourself more harm than continuing them."
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