

Insomnia is a known, but relatively infrequent, side-effect of
diphenhydramine.  

For most people, this does not occur.  On the other hand, most people
can build up a tolerance to an antihistamine with extended use.
(Allergy sufferers are often switched from one antihistamine to
another to avoid this.)


--
Steven Litvintchouk
MITRE Corporation
202 Burlington Road
Bedford, MA  01730-1420