Re: Why does smoking marijuana give you cottonmouth?

The active ingredient in Marijuana is a chemical called THC 
(tetrahydrocannabinol).  One of the things that THC does is act as an 
anticholinergic drug. Anticholinergics prevent the neurotransmitter 
acetylcholine from doing its thing. This causes different side effects, 
including dry mouth and dry skin (from decreased sweating), rapid heart 
rate and skin flushing. 
 http://www.postgradmed.com/issues/1999/10_01_99/johnson.htm

This article shows what happens when there is an overdose of a drug with 
anticholinergic side effects, for example, seen in an emergency room. 
Please note that these side effects won't be life-threatening in someone 
smoking marijuana. http://www.emedicine.com/EMERG/topic36.htm

Here is more information on marijuana:  http://www.nida.nih.gov/MarijBroch/Marijteens.html You should be able to 
find more information about drugs of abuse at http://www.nida.nih.gov/

Hope this helps.

Thanks for the good question.