What are the causes of xerostomia (dry mouth)?

Causes of Dry Mouth (Xerostomia)

Medications are the most common cause of dry mouth, particularly anticholinergic agents, antihypertensives, antidepressants, and diuretics, with polypharmacy exponentially increasing risk in elderly patients. 1, 2

Medication-Induced Causes (Most Common)

Anticholinergic Medications

• Centrally acting anticholinergics, tricyclic antidepressants, and cyclobenzaprine directly block acetylcholine receptors in salivary glands, reducing saliva production 1
• Antihistamines, antimuscarinics, anxiolytics, and antiparkinsonian agents all possess anticholinergic properties that diminish salivary flow 2, 3
• Over-the-counter products including decongestants and analgesics contribute to reduced saliva flow 1, 2

Cardiovascular Medications

• Beta-blockers (atenolol, metoprolol, propranolol) cause dry mouth through anti-adrenergic effects, with atenolol producing more pronounced effects 1
• Centrally acting antihypertensives like clonidine cause dry mouth as one of their most prevalent adverse effects through alpha-adrenergic mechanisms 1
• Diuretics and calcium channel blockers contribute to dry mouth and electrolyte disturbances 2, 3

Psychotropic Medications

• SSRIs, particularly fluoxetine at higher doses, cause dry mouth with greater frequency and severity at higher doses 1
• Bupropion commonly causes dry mouth as a side effect 1
• Antipsychotics possess anticholinergic properties that reduce salivation 2

Other Medications

• Opioids commonly cause dry mouth as an adverse effect 1
• Stimulant medications (phentermine, lisdexamfetamine) cause dry mouth in a significant percentage of users 1
• Anti-obesity medications (phentermine/topiramate, naltrexone/bupropion) list dry mouth as a common side effect 1
• Lithium and NSAIDs contribute to dry mouth and electrolyte disturbances 2, 3

Critical pitfall: Failing to review all medications including over-the-counter products is the most common missed diagnosis 3

Autoimmune and Systemic Disease Causes

Primary Autoimmune Conditions

• Sjögren's syndrome is characterized by lymphocytic infiltration of lacrimal and salivary glands, affecting approximately 0.4% of the population with a female-to-male ratio of 20:1 1
• The combination of dry mouth and dry eyes strongly suggests Sjögren's syndrome and warrants rheumatology referral 2, 3
• Sicca syndrome presents with abrupt onset dry mouth, usually without dry eyes, and can occur independently of Sjögren's syndrome 1
• Sicca complex is common in primary biliary cholangitis, though most patients have sicca symptoms rather than primary Sjögren's syndrome 1

Other Autoimmune Diseases

• Rheumatoid arthritis can cause salivary gland hypofunction 1
• Systemic lupus erythematosus is associated with xerostomia 1
• Scleroderma and psoriasis are associated with xerostomia 1

Endocrine and Metabolic Disorders

• Diabetes mellitus causes dry mouth through autonomic neuropathy and osmotic diuresis 3
• Thyroid dysfunction causes dry mouth, muscle weakness, and fatigue 3
• Chronic kidney disease is commonly associated with dry mouth in typical patient age ranges 1, 3
• Heart failure is associated with dry mouth 1

Radiation-Induced Xerostomia

• Head and neck radiation therapy causes radiation-induced dry mouth and painful mucositis through direct damage to salivary glands 1

Age-Related Factors

• Salivary flow rate declines with age, making older adults more susceptible to dry mouth even without other risk factors 1
• Elderly patients face substantially higher risk due to multiple medications combined with age-related decline in salivary flow 1
• Age-related sarcopenia of swallowing muscles diminishes oral clearance, contributing to the sensation of oral dryness 1

Neurological Conditions

• Parkinson's disease causes bradykinesia of swallowing muscles, leading to saliva pooling despite normal production and resulting in dry-throat sensation 1, 3
• Dementia is associated with dysphagia and related oral symptoms 1
• Stroke commonly leads to oropharyngeal dysphagia and associated oral dryness 1
• Multiple sclerosis affecting brainstem/cerebellum causes ataxia, fatigue, and autonomic dysfunction 3
• Bell's palsy, Riley-Day syndrome, and trigeminal neuralgia can contribute to dry mouth 1

Infectious and Hematologic Causes

• Hepatitis C and HIV can cause xerostomia 1
• Graft-versus-host disease and lymphoma can be associated with dry mouth 1

Additional Contributing Factors

• Fluid intake restrictions and dehydration from any cause worsen the perception and severity of xerostomia 1
• Autonomic dysfunction is strongly associated with dry mouth and can cause significant complications 1
• Mouth breathing (chronic or nocturnal) dries the oral mucosa 4
• Obstructive sleep apnea can be strongly associated with dry mouth symptoms and daytime somnolence 1
• Alcohol and caffeine consumption have diuretic effects that exacerbate xerostomia 2, 3

Important Diagnostic Considerations

• Rule out mimicking conditions such as candidiasis, burning mouth syndrome, and dysphagia, which can present similarly to xerostomia 1, 3
• Measure whole salivary flow rates objectively before initiating treatment, as the patient's subjective sensation may not correlate with actual salivary output 1, 3
• Differentiate true xerostomia from dysphagia-related pooling, as management strategies differ when dryness is due to clearance deficits rather than reduced production 1
• Notable exception: AChE inhibitors used for Alzheimer's disease actually increase saliva production, contrasting with most other medications 1