Xerostomia ( /ˌzɪərɵˈstoʊmiə/) is the medical term for the subjective complaint of dry mouth due to a lack of saliva. Xerostomia is sometimes colloquially called pasties, cottonmouth, drooth, or doughmouth. Several diseases, treatments, and medications can cause xerostomia. It can also be exacerbated by smoking or drinking alcohol.

Xerostomia can cause difficulty in speech and eating. It also leads to halitosis and a dramatic rise in the number of cavities, as the protective effect of saliva's remineralizing the enamel is no longer present, and can make the mucosa and periodontal tissue of the mouth more vulnerable to infection. Heavy methamphetamine use can cause xerostomia, usually called "meth mouth" in this case; it can be worsened by methamphetamine at recreational doses causing tight clenching of the jaw, bruxism (compulsive grinding of the teeth), or a repetitive 'chewing' movement as if the user were chewing, but without food in the mouth.

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