Diphenhydramine is one of the earliest antihistamines:

Being a first generation antihistamine, it has all the associated problems such as drowsiness and dry mouth. These are some of the least specific small molecule therapeutics you could hope for, which gives rise to many of the side effects. Interestingly, it has some effect on serotonin reuptake, which led to some drugs for depression with similar structure.

Molecules: You'd better learn to live with them.
Comments
Compare structure with second generation tricyclic antidepressant doxepin,
http://en.wikipedia.org/wiki/Doxepin
the only effective oral itch-suppressant for crispy critters (burn survivors). Two weeks of minimum dose to get over itching storms, then the side effects kick in (vegetabilization).
Posted by: Uncle Al | November 7, 2006 9:39 PM
That stuff will get me stoned. Hours of stream-of-consciousness burbling followed by drifting off to unconsciousness.
Posted by: Max Kaehn | November 7, 2006 10:55 PM
"Interestingly, it has some effect on serotonin reuptake, which led to some drugs for depression with similar structure."
One of the things I learned in the course of trying (more or less successfully) to find the right meds for my chronic depression is that some doctors will prescribe diphenhydramine as a "booster" for "regular" antidepressants. I've known a couple of people who have taken it for exactly that reason.
Posted by: anomalous4 | November 8, 2006 1:19 AM
Re anomalous4: diphenhydramine also has some anxiolytic effects that may enhance the effects of antidepressants in cases of comorbid anxiety and depression.
Posted by: Abel Pharmboy | November 8, 2006 12:48 PM