Need help with allergies—or sleeping? Be careful: A new study finds that some sleeping aids and allergy pills, including Benadryl and Nytol, are associated with an increased risk of developing Alzheimer's disease. The study looked at "anticholinergic" drugs, which block acetylcholine, a nervous system chemical transmitter, thus causing drowsiness and other side effects. They found that people who took at least 10mg per day of doxepin (a tricyclic antidepressant), 5mg per day of oxybutynin (like bladder control treatment Ditropan), or 4mg per day of diphenhydramine (the aforementioned Nytol and Benadryl) for more than three years were more likely to develop Alzheimer's or another form of dementia, the Guardian reports, noting that those would be considered "higher doses" of the drugs.
Why the link? It's not clear, but people with Alzheimer's have a shortage of acetylcholine, the transmitter these drugs block, and the researchers also note that in animals, anticholinergic effects are known to increase beta-amyloid protein levels, another characteristic of Alzheimer's. But, experts caution, it is still not known whether these drugs actually cause dementia, and the lead author of the study notes, "no one should stop taking any therapy without consulting their healthcare provider," though there are alternative therapies available that do not have anticholinergic effects, such as SSRI antidepressants and antihistamines like Claritin. Medical Daily notes that other common drugs, including cardiovascular and gastrointestinal medications, also have anticholinergic effects. (A recent study found that some lost memories could be restored.)