Anticholinergics are common drugs, CNN said. "Doctors, nurses and pharmacists need to work with older people and their carers to ensure that they only take medication if the benefits clearly outweigh the harms".
The study was funded by the Alzheimer's Society.
They analysed data from the UK's Clinical Practice Research Database for 40,770 patients aged 65 to 99 years who were diagnosed with dementia between April 2006 and July 2015.
Up to two million people in England are likely to be taking one of the anticholinergics identified by the study as linked to dementia at any one time, the authors said.
Several studies have reported associations between use of anticholinergics and future cognitive decline and dementia, but it is not clear whether this is due to the drugs themselves or the underlying conditions for which they were prescribed. "But we broke it down by class, which is where our study really has its novelty and power".
The study also analyzed over 27 million prescriptions.
Not taking prescribed drugs could have serious consequences, Dr Maidment said.
This means those patients with a new dementia diagnosis had significantly more exposure to anticholinergic medications during the study period than those without dementia, according to Savva.
Examples of frequently-prescribed anticholinergic antidepressants include Amitriptyline, Dosulepin and Paroxetine.
Long-term use of certain anti-depressants have been linked to dementia in a large British study, although researchers could not definitively conclude that the drugs were the cause.
However, the risk does appear to increase with long-term use of stronger drugs.
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"But it's hard to generalize across patients, and it's hard to talk about an individual because this is a population average risk and it depends very much on the patient", he added.
Hundreds of thousands of people are taking routine medicines that increase their risk of dementia by up to a third, researchers have warned.
The researchers, who report their findings in the British Medical Journal, investigated GP records for more than 40,000 people over the age of 65 with dementia and almost 300,000 without dementia.
Prof Chris Fox, Professor of Clinical Psychiatry at UEA's Norwich Medical School and Consultant Psychiatrist, said: "While the associations are moderate, given the high incidence of dementia, they reflect a potentially important risk to patients".
"But the headline claim that some drugs, especially antidepressants, can cause dementia up to 20 years later should be looked at closely".
"There is also some animal evidence that anticholinergics may affect neuroinflammation", he said.
The study, led by a team at the University of East Anglia in the United Kingdom, involved a collaboration between teams in the United Kingdom, US and Ireland."These findings make it clear that clinicians need to carefully consider the anticholinergic burden of their patients and weigh other options", claims Malaz Boustani, M.D., MPH, a Regenstrief Institute and Indiana University (IU) Center for Aging Research investigator, and co-author of the researchers' published paper in the BMJ.
"Clinicians should continue to be vigilant with respect to the use of anticholinergic drugs, and should consider the risk of long-term cognitive effects, as well as short-term effects, associated with specific drug classes when performing their risk-benefit analysis".
This is an observational study, so no firm conclusions can be drawn about cause and effect, and the authors outline some limitations, such as possible misclassification of dementia cases and a lack of information on depression severity. "And the association with dementia increases with greater exposure to these types of medication".
"Of particular interest to us is the classes where there is no association".
The adjusted OR for any anticholinergic drug with an ACB score of 3 being associated with dementia was 1.11 (95% CI 1.08-1.14, P 0.01), but drugs for gastrointestinal and respiratory conditions were not linked with dementia risk.