"3.5 Any long-term effects?
Rumors persist of brain/stomach damage resulting from frequent use of diphenydramine HCl and similar drugs. Chronic users seem to be depressed most of the time, but they seem to recover when they stop doing the drug. Also there is a risk of liver/kidney damage. Since it is not addictive, you don't really run a risk of frequent use; however, exercise control when taking it and don't take it too frequently... the results may be devastating. "
http://leda.lycaeum.org/?ID=13358
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