Xerostomia, or dry mouth, is caused by methamphetamine and at least 430 prescription drugs. These drugs act directly on the nervous system to reduce the flow of saliva from three sets of glands and many very small glands that serve the mouth.

Dry mouth by itself can be the cause of very agressive tooth decay known as "rampant decay". Saliva serves an important function to rinse away bacteria from teeth, and to dilute acid waste products of the bacteria that cause decay.

Dry mouth can be aggravated when meth abusers get dehydrated. Some users have to be hospitalized to treat dehydration.

A pharmacist can help those who suffer from dry mouth with a variety of over the counter (OTC) products that act as "saliva substitutes."