STANFORD (CBS SF) — There is growing evidence to suggest the long-term use of some very common over-the-counter medicines — from pain relievers, cold and allergy treatments even some sleep aids — may increase your risk of dementia.

Crammed inside a drawer at Lori Beth Eisenstadt’s home in the East Bay, you’ll find many over-the-counter medications for colds, coughs and allergies.

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“This is pretty much everything that we use on a somewhat regular basis,” explained Eisenstadt.

Many of these products include an antihistamine known as diphenhydramine, commonly sold as Benadryl.

“Everybody knows Benadryl. It’s a mom’s standby. Whether you have your own child or you have a child visiting, if there is a kid who has an allergy, you always have Benadryl standing by,” said Eisenstadt, who is both a mother and teacher.

If you use Benadryl or many of the popular sleep aids that contain diphenhydramine — which is found in Tylenol PM,  Advil PM, Sominex or ZZZquil — or a different drug called doxylamine, the active ingredient found in Unisom, then you’re using a class of drug called an anticholinergic drug.

Anticholinergics block the action of an important neurotransmitter that’s used by our nervous system and brain.

Blocking that action can cause drowsiness and confusion. But now there’s evidence to suggest their long term use may increase the risk of dementia, even cause irreparable harm.

“I would take these medications myself only very rarely. And I will try at all costs to avoid taking them for a long term,“ said Dr. Barbara Sommer

Doctor Sommer is a geriatric psychiatrist emerita at Stanford Medical Center and an expert on anticholinergic drugs.

She has reviewed the most recent research, two medical reports published within the last two years. The first was a study done by researchers at the University of Washington in 2015. A second more recent study from the University of Indiana was published last month in the Journal of the American Medical Association’s Neurology.

“I think we’re starting to see a real story now,” said Doctor Sommer

In the most recent report, older adults who took anticholinergics over the long term — continuously for years — performed worse on tests that measured short-term memory, verbal reasoning, planning and as problem solving.

PET scans revealed their brains were less active, while MRI scans showed their brains had atrophied or shrunk.

“Whereas it’s always be thought if you stop anticholinergic drugs, all of the cognitive functions you’ve lost come back, now people aren’t so sure. And they’re worried that this may lead to or hasten the onset of dementia,” explained Doctor Sommer.

However, these studies do not prove a cause and effect.

The Consumer Healthcare Products Association or CHPA is the trade group that represents the makers of these over-the-counter products. The CHPA says the study involved a relatively small sample of participants taking medications with anticholinergic properties and that this group of patients relied on self-reported medication use.

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As for anticholinergic drugs, the CHPA points out that the active ingredients are approved to treat occasional sleeplessness by the FDA and recognized as safe and effective when taken as instructed.

And the labels offer clear instruction on how the medications should be taken. They are not intended to be taken for more than two weeks at a time and are definitely not meant to be taken continuously for long periods.

The CPHA says the most important step for consumer when taking any OTC is to always read and follow the label. Consumers should talk to their healthcare providers if their sleeplessness persists or if they have any questions.

Sommer says diphenhydramine is a great medication for acute allergy, rash, or hives. However, she cautions that patients don’t want to use it or other anticholinergics on a daily basis for months at a time.

If you do, you need to consult your doctor and weigh the risks versus the benefits.

“There are other ways to treat insomnia. And some of them don’t have to do with medications at all. They have to do with modifying behaviors,” said Sommer.

As for Eisenstadt, she is already weighing the options, like not drinking coffee late in the day.

“Rather than turning to a sleep aid, I’d rather just modify my habits,” she explained.

KPIX News contacted the US FDA and a spokeswoman said that generally, the FDA does not comment on specific studies, but evaluates them as part of the body of evidence to further the agency’s understanding about a particular issue and to assist in the FDA’s mission to protect general health.

The FDA is reviewing the findings of the papers. The agency added that diphenhydramine is generally recognized as safe and effective for use in nighttime sleep aids.

In addition to over-the-counter drugs, there are prescription drugs that are anticholinergic as well.

Indiana University Center for Aging Research has developed an Anticholinergic Cognitive Burden Scale or ACB.

On this list, the definitive anticholinergic drugs are scored as a “2” or “3.” Possible anticholinergics have a score of “1”.

The Center says for each definitive anticholinergic drug that you take that’s on the list and scored as a 2 or 3, you may increase your risk of cognitive impairment by 46 percent over 6 years.

If you take any of these drugs on a regular basis, the benefit may outweigh the risk and you should discuss with your doctor. You may also want to see if there is an effective alternative.

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You can learn more about the study of anticholinergics and their effects at the links below: