A new study of more than 283,000 elderly people in the UK has found that long-term use of anticholinergic drugs – including some medications for depression, epilepsy, and Parkinson's disease – is associated with a significant increased risk of dementia.

For the study, which was funded by the National Institute for Health Research, researchers from the University of Nottingham, UK, tracked more than 58,000 with dementia and 225,000 people without it.

The time period included in the study spanned up to 20 years, beginning before any of the participants were diagnosed with dementia.

The researchers found that patients who took even one strong anticholinergic drug at the minimum effective daily dose for three years had a 50 percent greater likelihood of being diagnosed with dementia, even when taking into account other factors like participants' age, gender, and whether or not they smoked or drank alcohol.

The study also found that the link between these drugs and dementia was stronger in people diagnosed before age 80, suggesting that middle-aged and elderly people should be even more cautious about their medications.

The study authors don't say that people should stop taking anticholinergic medications. Rather, they recommend doctors weigh the pros and cons of these drugs before prescribing them, and consider alternative treatment options when possible, particularly when patients are in middle age and beyond.

'Anticholinergic drugs' are a common class of drugs that block a specific brain chemical, and not all are implicated in dementia risk

Overall, the study included 56 anticholinergic medications. The term describes a class of drugs used to help manage muscle spasms and other involuntary muscle movements.

The drugs work by blocking a specific neurotransmitter, acetylcholine, that the brain uses to tell muscles in the lungs, gastrointestinal tract, urinary tract, and other areas of the body to contract.

  • As a result, people can improve digestive, urinary, and other types of functioning when on the drugs. Some antidepressants, epilepsy drugs, and medications used for bladder control are anticholinergic drugs that the study found were associated with an increased dementia risk. They include:
  • Antidepressants like amitriptyline, paroxetine, nortiptyline, and doxepin
  • Antiepileptics like carbamazepine and oxcarbazepine
  • Antipsychotics like quetiapine, olanzapine, chlorpromazine, and perphenazine
  • Drugs for Parkinson's disease like benztropine, orphenadrine, and trihexyphenidyl
  • Medications for bladder control including darifenacin, fesoterodine, oxybutynin, and tolterodine

Not all types of anticholinergic drugs included in the study were implicated in demetia risk, however. Researchers found no correlation between dementia rates and other anticholinergic medications, including:

  • Antihistamines like diphenhydramine and hydroxyzine
  • Gastrointestinal antispasmodics like dicyclomine and hyoscinepropantheline
  • Antimuscarinic bronchodilators like ipratropium
  • Antiarrhythmics like disopyramide
  • Skeletal muscle relaxants like tizanidine and methocarbamol

This isn't the first study finding a link between anticholinergics and dementia, but more research is still needed

These findings are supported by previous research on possible correlations between dementia and anticholinergics. Past studies included smaller group of patients, and focused on short-term exposure to the drugs but had a similar result: a significant increase in risk of dementia associated with anticholinergics.

Some of the underlying conditions treated by anticholinergics, like depression, have their own links to dementia, so it's hard to understand whether it's the illnesses, the drugs that treat them, both, or something else entirely that's to blame.

However, the study's authors theorise that if a causal link could be proven with more research, up to 10 percent of dementia diagnoses could be attributable to anticholinergic exposure.

This would make it among the major risk factors for dementia along with smoking (14 percent of dementia cases are linked to later-life smoking), physical inactivity (6.5 percent), midlife hypertension (5 percent), and diabetes (3 percent).

This article was originally published by Business Insider.

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