Doctors often prescribe anticholinergic drugs for a variety of ills. But a new study suggests they may increase the risk of dementia in older patients.

These medicines include everything from Benadryl (diphenhydramine) to certain antipsychotics and Parkinson's meds. They're used to treat a wide range of other conditions, including depression, chronic obstructive pulmonary disease, overactive bladder, allergies, and gastrointestinal disorders.

Anticholinergic drugs help contract and relax muscles, and work by blocking acetylcholine, a chemical that transmits messages in the nervous system.

But the new British study found that people aged 55 and older who took strong anticholinergic medications daily for three years or more had a 50% increased risk of dementia.

"Our study adds further evidence of the potential risks associated with strong anticholinergic drugs, particularly antidepressants, bladder antimuscarinic drugs, anti-Parkinson drugs and epilepsy drugs," said study author Carol Coupland. She works in the division of primary care at the University of Nottingham.

Anticholinergics are known to cause short-term side effects -- including confusion and memory loss -- but it's unclear if long-term use increases the risk of dementia.

To find out, Coupland's team examined the medical records of nearly 59,000 patients in the U.K. with dementia, as well as a control group of more than 225,000 patients without dementia. All the patients were 55 and older. The average age of the dementia patients was 82.

Overall, they study found an increased risk of dementia among those who took anticholinergic drugs. After accounting for other risk factors for dementia, the researchers concluded that strong anticholinergic meds were associated with an increased risk of dementia.

There was no increased risk of dementia among patients who took other types of anticholinergic drugs such as antihistamines (Benadryl) and gastrointestinal drugs.

In the one to 11 years before dementia diagnosis or the equivalent in controls, nearly 57% of dementia patients and 51% of people in the control group were prescribed at least one strong anticholinergic drug, with an average of six prescriptions in dementia patients and four in controls.

The study was published June 24 in the journal JAMA Internal Medicine.

The researchers noted that this was an observational study, so it cannot prove that anticholinergic drugs help cause dementia. For example, it's possible that the drugs were prescribed to dementia patients to help treat very early symptoms of the disease.

However, if anticholinergics do help cause dementia, about 10% of dementia cases might be attributable to the drugs, the study authors said.

At the very least, "this study provides further evidence that doctors should be careful when prescribing certain drugs that have anticholinergic properties," study co-author Tom Dening, head of Nottingham's Center for Dementia, said in a university news release.

He stressed, however, that "it's important that patients taking medications of this kind don't just stop them abruptly, as this may be much more harmful. If patients have concerns, then they should discuss them with their doctor to consider the pros and cons of the treatment they are receiving."

And Coupland stressed that, "the risks of this type of medication should be carefully considered by health care professionals alongside the benefits when the drugs are prescribed." In some cases, "alternative treatments should be considered where possible, such as other types of antidepressants or alternative types of treatment for bladder conditions," she said.

Coupland added that, "we found a greater risk for people diagnosed with dementia before the age of 80, which indicates that anticholinergic drugs should be prescribed with caution in middle-aged people as well as in older people."

Dr. Gayatrii Devi is a neurologist specializing in memory disorders at Lenox Hill Hospital in New York City. She believes many people too easily resort to anticholinergics for sleep complaints, especially.

"There is an increasing epidemic of reliance on sleeping medications, from benzodiazepines including medications like Ambien and Xanax, to anticholinergics commonly used in many over-the-counter sleep aids, to power ourselves off at night," she said.

Devi believes there are other behavioral ways to resume getting a good night's sleep.

"Ideally, what we want to do is to go back to something we were born experts at -- sleeping," Devi said, "without any sleep medications."

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