Given the risks, older adults should look for drugs that don't contain benadryl, he said.
"A lot of these medications are not recognized for these side effects," he contended. "It's time for the FDA to start taking this negative impact of these medications on the aging brain seriously."
The report is published in the May online issue of the Journal of Clinical Interventions in Aging.
According to Boustani, researchers in brain pharmacoepidemiology at Indiana University's Center for Aging Research is conducting a study of 4,000 older adults to see if the long-term use of medications with anticholinergic effects is associated with the development of severe cognitive impairment, such as Alzheimer's disease.
Dr. Clinton Wright, an associate professor of neurology at the Miller School of Medicine at the University of Miami, agreed that more study is needed to assess the effects of these drugs on the brain.
"These findings don't surprise me at all," Wright said. "People tend not to think of their OTC medications as medication, but any medication that has anticholinergic effects can affect people's cognition."
Wright believes the drugs should carry a warning of this potential side effect.
Deborah G. Bolding, a spokeswoman for GlaxoSmithKline, the maker of Sominex, defended the product and said it complies with all current FDA regulations. However, she would not comment specifically on whether diphenhydramine is associated with an increased risk of delirium in older adults.
"Sominex is a mild sleep aid designed to help individuals through periods of nervous tension or stress, which are accompanied by sleeplessness. It has been proven safe and effective in medical tests when taken as directed, and has been safely used by millions of satisfied customers," Bolding said.
"For all formulations, Sominex
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