A: Dry mouth or "xerostomia" is due to insufficient secretion of saliva. This happens to everyone occasionally; you're most likely to notice dry mouth if you're nervous or under stress. But dry mouth that is more long lasting is most likely to be a drug side effect. Hundreds of drugs, illicit, prescription and over-the-counter, can cause dry mouth. The commercial ones usually responsible are decongestants, diuretics and other blood pressure medications, antidepressants, antihistamines, muscle relaxants, drugs for urinary incontinence, and those used to treat Parkinson's disease. If you take one of these or any other drug regularly, ask your doctor or pharmacist to suggest an alternative that doesn't cause dry mouth.
Dry mouth can also be a symptom of an autoimmune disease such as rheumatoid arthritis or Sjogren's syndrome or related to conditions like diabetes and Parkinson's disease, and it is a common and unpleasant side effect of radiation therapy to the head and neck. If you are having trouble chewing, that, too, can lead to dry mouth. Dry mouth is more than just an uncomfortable annoyance; it can lead to serious dental problems. Saliva helps prevent tooth decay by washing food and plaque off of your teeth. It also limits the growth of bacteria that can damage tooth enamel and cause gum disease. Your dentist or physician may recommend medication to stimulate the flow of saliva if your problem doesn't resolve. Here are some other suggestions that may help:
Sip water frequently during the day, and keep a glass of water at your bedside at night. Adding a little lemon juice can help stimulate saliva flow.
Avoid both salty and sugary foods.
Avoid alcohol (and mouthwashes containing alcohol), caffeine and tobacco. All can dry the mouth.
Suck on sugar-free hard candy or chew sugarless gum to improve your saliva flow. (the sweetener Xylitol helps reduce cavities, but avoid lemon-flavored hard candy - it turns saliva acidic, which increases the risk of tooth decay.)
Use a humidifier at home.
Try commercial saliva substitutes - available at drugstores - to help keep your mouth moist.
While you're dealing with dry mouth, make an extra effort to keep your teeth and gums in good shape: Be sure to brush twice a day and floss daily to prevent plaque build-up, and have your teeth and gums checked regularly.
Andrew Weil, M.D.