As reported by the New York Times (https://www.nytimes.com/2026/04/22/well/mind/medications-dementia-risk-increase.html), there is strong evidence that antihistamines are associated with increased dementia risk. These medications, called anticholinergics, work by blocking the activity of the neurotransmitter acetylcholine, which is important for attention and memory. Antihistamines such as ZzzQuil, Unisom, Tylenol PM, Sominex, and Benadryl are used as over-the-counter sleep aids and are one of the most common types of anticholinergics. In the short term, anticholinergics can cause drowsiness and memory impairment. In the long term, several meta-analyses suggest they are associated with an increased dementia risk of about 50% in a dose-response relationship (i.e., the greater the use, the great the risk). The greatest risk is among people who take this type of medication daily for multiple years vs. once-in-a-while use which is unlikely to increase dementia risk. The American Geriatric Society recommends that older adults also avoid antihistamines because the medications can also cause falls.
