Xerostomia is the medical term for a dry mouth due to a lack of saliva. Xerostomia is sometimes colloquially called pasties, cottonmouth, or doughmouth.

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 of the mouth more vulnerable to infection. Notably, a symptom of heavy methamphetamine use usually called "meth mouth" is largely caused by xerostomia which is worsened by the fact that methamphetamine at recreational doses can cause tight clenching of the jaw, bruxism (compulsive grinding of the teeth), or a repetitive 'chewing' movement like the user is chewing without food in the mouth. Also people^[who?] who prolong or 'binge' use of methamphetamine sometimes do not give the same amount priority to hygiene as they would without the methamphetamine.
 

It may be a sign of an underlying disease, such as Sjögren's syndrome, poorly controlled diabetes, or Lambert-Eaton syndrome, but this is not always so.

Other causes of insufficient saliva include anxiety, medications, or the consumption of alcoholic beverages, physical trauma to the salivary glands or their ducts or nerves, dehydration caused by lack of sufficient fluids, excessive breathing through the mouth, previous radiation therapy, and also a natural result of aging, other conditions or factors not mentioned also can have the ability to cause dry mouth. The vast majority of elderly individuals will suffer xerostomia to some degree. Playing or exercising a long time outside on a hot day can cause the salivary glands to become dry as the bodily fluids are concentrated elsewhere. Xerostomia is a common side-effect of various drugs, such as Cannabis (Cotton Mouth), and can also occur with other drugs and herbs that are smoked because smoke can dry out the mouth, amphetamines, antihistamines, some antidepressants, and there are other drugs that may cause xerostomia.