What causes dry mouth (xerostomia) in older adults, especially those with a history of diabetes, Sjögren's syndrome, or undergoing chemotherapy or radiation therapy?

Causes of Dry Mouth (Xerostomia)

Medications are the most common cause of dry mouth in older adults, with anticholinergic drugs, polypharmacy, antidepressants, antihypertensives, and opioids being the primary culprits. 1, 2

Medication-Related Causes

The anticholinergic burden from multiple medications substantially increases dry mouth risk, particularly in older adults taking several drugs simultaneously. 1

High-Risk Medication Classes:

• Anticholinergic agents directly block muscarinic receptors, with centrally acting drugs like scopolamine and atropine causing the most pronounced effects 1, 3
• Tricyclic antidepressants have significant anticholinergic properties making them frequent offenders 1, 3
• SSRIs, especially fluoxetine at higher doses, cause dry mouth with severity correlating to dose 3
• Antihypertensives including beta-blockers (atenolol, metoprolol, propranolol) through anti-adrenergic effects, and centrally acting agents like clonidine through alpha-adrenergic mechanisms 1, 3
• Opioids commonly produce xerostomia as an adverse effect 1, 3
• Muscle relaxants such as cyclobenzaprine cause dry mouth as one of their most common reactions 1
• Stimulants and anti-obesity medications including phentermine, lisdexamfetamine, and combination products like phentermine/topiramate 1
• Other common culprits include antihistamines, analgesics, antipyretics, antibiotics, and bupropion 1, 3

Disease-Related Causes

Autoimmune Conditions:

• Sjögren's syndrome involves lymphocytic infiltration of salivary and lacrimal glands, affecting approximately 0.4% of the population with a 20:1 female-to-male ratio 1
• Sicca syndrome presents with abrupt onset dry mouth, usually without dry eyes, and occurs independently of Sjögren's syndrome 1, 3
• Rheumatoid arthritis can cause salivary gland hypofunction 1

Other Systemic Diseases:

• Diabetes mellitus contributes to reduced salivary flow 4
• Radiation therapy to the head and neck causes direct damage to salivary glands 5, 4
• Chemotherapy affects salivary gland function 5

Age-Related Factors

Normal aging causes a decline in salivary flow rate, making older adults inherently more susceptible to dry mouth even without other risk factors. 6, 1 This age-related reduction, combined with polypharmacy common in elderly patients, creates substantially higher risk. 1, 3

Additional Contributing Factors

• Dehydration from any cause worsens xerostomia perception and severity 3
• Fluid intake restrictions compound medication-induced dry mouth 3
• Chronic mouth breathing diminishes salivation 4
• Alcohol and caffeine intake exacerbate symptoms 2, 4

Important Clinical Caveats

Rule out conditions that mimic xerostomia: candidiasis, burning mouth syndrome, and dysphagia can present similarly but require different management. 1, 3 Some conditions may increase saliva in the mouth due to reduced clearance, mimicking hypersalivation despite actual reduced production. 3

Note the paradoxical effect: AChE inhibitors used for Alzheimer's disease actually increase saliva production, contrasting with most other medications. 1, 3