Most often, chronic dry mouth is caused by:
Side effect of drug therapy. More than 400 medicines can cause the salivary glands to make less saliva. Medications used to treat hypertension, anxiety, depression or psychosis cause the most difficulty. Antihistamines, antispasmodics, cancer-chemotherapy drugs, decongestants, and muscle relaxants often cause dry mouth.
Health conditions such as extensive radiation therapy to the face and neck can cause severe dry mouth.
Many disease effect saliva flow: Sjogren's syndrome*, bacterial and viral infections, poorly controlled diabetes, salivary-gland stones, tumors, Alzheimer's disease, diabetes, anxiety, HIV/AIDS, depression, Bell's palsy, and Parkinson's disease. Alzheimer's and stroke can not feel the wetness in their mouth.
Chemotherapy drugs that are used to treat cancer can make saliva thicker causing the mouth to feel dry.
Poorly controlled diabetes may result in a neuropathy to these glands and a subsequent decrease in secretions leading to dry mouth.
Nerve damage from an injury to the head or neck that tell salivary glands not to make saliva.
Attachment loss from periodontal disease or who have had root caries are especially vulnerable to the adverse effects of xerostomia.