Methamphetamine (Meth) has minimal direct toxic effect on the mouth. However, its subcomponents lead to a constellation of side effects that result in what you are describing as “Meth Mouth.”
The chemical residues in meth that remain from its production are corrosive to the teeth and irritate the soft tissue within the mouth sometimes causing ulcers. The most damaging effect of meth on dental hygiene due to its drying of the salivary glands. Without saliva, acidic materials dissolve away tooth enamel. Bacterial overgrowth occurs without saliva to keep the mouth flora in check resulting in gingivitis and cavities. Methamphetamine also causes constriction of blood vessels in the oral and nasal cavities resulting in atrophy of the gums, nerve death, and loosening of the teeth. Therefore, “Meth Mouth” is a result of toxic chemical residues irritating the mouth, decreased saliva production, and constriction of blood vessels.
As with all patients, proper dental hygiene is required to prevent gingivitis and cavities. Dry mouth can be prevented with oral saliva-replacement sprays. But the most important step for the health of your friend is to abstain from using methamphetamine.