Long term use of certain drugs has long been known to have a negative effect on cognition, and may increase a person's risk for dementia.

Findings of a new study, however, have pinpointed particular classes of drugs that cause the degenerative condition.

In the study published in the British Medical Journal on Wednesday, researchers discovered the anticholinergic drugs that may increase risk for dementia.

Anticholinergic Drugs

Anticholinergic drugs work by blocking the effects of the neurotransmitter acetylcholine, which is released to send signals to other cells. These drugs are prescribed to 20 percent to 50 percent of older adults in the United States who suffer from a range of neurological, gastrointestinal, psychiatric, respiratory, and muscular conditions.

Using data from UK's Clinical Practice Research Database to study the risk of dementia in nearly 350,000 adults, the researchers found that individuals who used certain types of anticholinergics, such as those used to treat depression, urinary incontinence, and Parkinson's disease, for at least a year or more had about 30 percent increased risk of dementia.

Those taking other classes of anticholinergics, such as those used for gastrointestinal issues, on the other hand, did not have increased odds of developing the neurological disease.

"A robust association between some classes of anticholinergic drugs and future dementia incidence was observed. This could be caused by a class specific effect, or by drugs being used for very early symptoms of dementia," study researcher Louise Robinson, the Director of Newcastle University's Institute for Ageing, and colleagues wrote in their study.

Antidepressants And Dementia

Researchers said that they found a link between use of anticholinergic antidepressants and dementia, even when these drugs are taken 20 years prior to diagnosis. Frequently prescribed anticholinergic antidepressants include Dosulepin, Paroxetine, and Amitriptyline.

Figures from the U.S. Centers for Disease Control and Prevention show that one in every eight people in the United States over 12 years old have used antidepressant. The CDC also said that long-term use of these drugs is common.

"One-fourth of all people who took antidepressants in the past month reported having taken them for 10 years or more," the CDC said.

Identifying Drugs Linked To Increased Dementia Risk

The findings of the new study suggest that if someone already has risk of developing dementia, that risk would increase with long-term use of certain anticholinergic medications. Robinson said that the findings help doctors decide which drugs can be safely used long term as people age.

"This study provides important new evidence around the role of certain drugs in influencing impaired cognition in older people," the researcher said.