Dry mouth, also called xerostomia, is a common side effect of many drugs and medications, including marijuana. In the past, some people believed that dry mouth was caused by inhalation of irritating smoke. However, we now know that marijuana affects the salivary glands directly. This explains why you can get dry mouth even if you vaporize or eat marijuana products.
Marijuana causes dry mouth because the cannabinoid in THC and CBD, the active ingredient in cannabis, binds to receptors in the salivary glands and causes them to be less active. The higher the percentage of THC and CBD, the worse the symptoms.
Cannabinoid receptors are found on the submandibular glands — a pair of glands located beneath the floor of the mouth that are responsible for producing about 70% of our saliva. When the cannibinoid binds to these receptors, messages from the parasympathetic nervous system that normally tell the submandibular glands to produce saliva are blocked. This means the glands produce less saliva, resulting in a dry mouth.