People take Benadryl for different reasons — to combat allergies or help them fall asleep, for example — but research suggests that long-term use of the drug may be linked to serious mental health conditions.

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A 2016 study published in JAMA Neurology found that the active ingredient in Benadryl, diphenhydramine, appears to impair cognitive functioning and increase the risk of dementia for individuals who take the drug in high doses or as a long-term treatment option. According to CNN, the study was the first to identify physical changes in the brains of those who use so-called anticholinergic drugs, which are found in over the counter medicines like "Benadryl, Demerol, Dimetapp, Dramamine, Paxil, Unisom and VESIcare."

"These findings might give us clues to the biological basis for the cognitive problems associated with anticholinergic drugs, but additional studies are needed if we are to truly understand the mechanisms involved," Dr. Shannon Risacher, one of the study's co-authors, said in a press release.

ATTN: reached out to Benadryl for comment, but a representative was not immediately available.

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While earlier research has indicated that Benadryl may be associated with increased risk of dementia, researchers at the Indiana University School of Medicine used brain imaging techniques and determined that people who take anticholinergic drugs such as diphenhydramine show reduced brain size and lower metabolism. These biological indicators could explain why the drug appears to have an effect on mental health, researchers say.

A 2015 study published in JAMA Internal Medicine set the stage for this study.

Researchers at the University of Washington released a study that looked at nearly 3,500 seniors involved in a seven-year program known as the Adult Changes in Thought (ACT). Eight hundred participants developed dementia over the course of the study and by examining prescription records and self-reported information about individuals' medical history, researchers were able to establish a strong link between dementia and the use of anticholinergic drugs such as Benadryl.

"Older adults should be aware that many medications — including some available without a prescription, such as over-the-counter sleep aids — have strong anticholinergic effects," Dr. Shelly Gray, the lead author of the study, said in a press release. "And they should tell their health care providers about all their over-the-counter use."

It's important to note that these studies do not show links between short-term use of Benadryl and increased risk of dementia.

Indiana University School of Medicine - sciencedaily.com

The 2015 study assessed the effects of long-term anticholinergic drug use on people 65 or older, and it found that the risk of dementia increased when seniors took these drugs for more than three years. That doesn't necessarily mean that short-term use of the drug is safe, but these studies specifically concern long-term use, CBS News reports.

"If providers need to prescribe a medication with anticholinergic effects because it is the best therapy for their patient, they should use the lowest effective dose, monitor the therapy regularly to ensure it’s working, and stop the therapy if it’s ineffective," Dr. Gray said in a press release.

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