For anyone considering regular recreational benadryl use, please read this link:
This study examines OTC anticholinergics use in a group of 3500 people 65 and older in Seattle, Washington at two points in time, an average of 7 years apart.
In that time, 800 individuals developed dementia and they found that anticholinergic use resulted in an increased risk of dementia. There is a dose-dependent relationship as well, the higher the cumulative dose meant a greater risk of developing dementia.
From the article:
"Taking an anticholinergic for the equivalent of three years or more was associated with a 54% higher dementia risk than taking the same dose for three months or less."
Granted, this study is looking at persons 65 and older, which do have an altered drug metabolism compared to younger persons, but even so it's not looking good generally for humans to have chronic exposure to drugs like Benadryl.