What causes a bitter taste in the mouth?

Bitter Taste in the Mouth: Causes and Clinical Approach

Bitter taste in the mouth most commonly results from medication side effects, particularly with drugs that activate bitter taste receptors (TAS2Rs), followed by oral/dental pathology, neurological conditions affecting taste pathways, and systemic disorders affecting salivary function.

Medication-Related Causes (Most Common)

Many pharmaceuticals directly activate bitter taste receptors (TAS2Rs) both in the oral cavity and systemically, causing persistent bitter taste perception. 1, 2

Common Culprit Medications:

• Proton pump inhibitors: Omeprazole causes taste perversion in 10-15% of patients, particularly when combined with clarithromycin 3
• Antibiotics: Clarithromycin, erythromycin, and ofloxacin are known TAS2R activators 1
• Psychiatric medications: Haloperidol activates bitter receptors 1
• Antimalarials: Chloroquine is a potent TAS2R agonist 1
• Cardiac medications: Procainamide stimulates bitter taste receptors 1
• Intranasal antihistamines: Azelastine and olopatadine commonly cause bitter taste as a side effect (reported in product labeling) 4
• Anticholinergic medications: Can impair taste function through reduced salivary flow 5

Mechanism:

Bitter-tasting drugs activate TAS2R receptors not only in the mouth but also in extraoral locations including the gastrointestinal tract, respiratory system, and other tissues, leading to systemic bitter taste perception 1, 6, 2

Oral and Dental Causes

Invasive dental procedures can damage the chorda tympani nerve or lingual nerve, resulting in taste alterations including persistent bitter taste. 7

Specific Dental Triggers:

• Third molar extractions: Particularly unerupted mandibular third molars pose highest risk 7
• Local anesthetic injection: Direct needle trauma or neurotoxic effects can damage taste nerves 7
• Lingual flap retraction: During surgical procedures in the posterior mandible 7
• Oral candidiasis: Can cause mucosal changes affecting taste 4

Neurological Causes

Burning mouth syndrome (BMS) presents with burning sensations but can include abnormal taste (dysgeusia) as an associated feature, predominantly affecting peri- and post-menopausal women. 4

Key Features of BMS:

• Continuous burning sensation of tongue, lips, palate, or buccal mucosa 4
• Normal-appearing oral mucosa on examination 4
• Associated dry mouth and abnormal taste in many cases 4
• Represents a disorder of peripheral nerve fibers with central brain changes 4
• Poor prognosis with only small percentage achieving full resolution 4

Other Neurological Considerations:

• Post-traumatic trigeminal neuropathy: Following dental procedures or facial trauma, can cause taste disturbances 4
• Stroke and neurodegenerative diseases: Can affect taste pathways 5

Age-Related and Systemic Factors

Normal aging causes alterations in olfaction and gustatory sensation, with decreased salivary flow contributing to taste disturbances. 5

Age-Related Changes:

• Decreased force generation of oral tongue muscles 5
• Lower salivary flow rates leading to xerostomia 5
• Changes in olfaction affecting overall taste perception 5

Genetic Factors

Polymorphisms in bitter taste receptor genes, particularly TAS2R38, influence individual sensitivity to bitter compounds and may predispose to taste complaints. 4

Patients can be phenotyped as supertasters, intermediate tasters, or non-tasters based on their TAS2R38 genotype 4

Clinical Evaluation Algorithm

Step 1: Medication Review

• Review all current medications, particularly those listed above as common TAS2R activators 3, 1
• Consider temporal relationship between medication initiation and symptom onset 3
• Trial discontinuation or substitution of suspected offending agents when clinically appropriate 4

Step 2: Oral Examination

• Inspect for oral candidiasis, mucosal lesions, or signs of recent dental work 4
• Assess for xerostomia (dry mouth) 4, 5
• Document any areas of sensory changes or allodynia 4

Step 3: Exclude Secondary Causes

• Hematological screening: Complete blood count to exclude disorders affecting taste 4
• Autoimmune evaluation: If clinically indicated 4
• Endocrine assessment: Particularly in peri/post-menopausal women with BMS 4

Step 4: Neurological Assessment

• Evaluate for history of head trauma, stroke, or neurodegenerative disease 5, 7
• Perform qualitative sensory testing if neuropathic cause suspected 4
• Consider MRI if focal neurological deficits present 4

Management Approach

Primary Interventions:

• Discontinue or substitute offending medications when possible 3, 1
• Treat underlying oral pathology: Antifungal therapy for candidiasis 4
• Optimize salivary flow: Address xerostomia with saliva substitutes or stimulants 5

For Burning Mouth Syndrome:

• Reassurance and education: Inform patients the condition will not worsen 4
• Cognitive behavioral therapy: First-line approach 4
• Neuropathic pain medications: May provide benefit in selected cases 4

Critical Pitfalls to Avoid

• Do not overlook medication-induced causes: This is the most common reversible etiology 3, 1
• Do not assume all bitter taste is benign: Rule out serious neurological conditions in patients with acute onset or associated neurological symptoms 4, 7
• Do not dismiss patient complaints: Even when oral mucosa appears normal, conditions like BMS can significantly impact quality of life 4
• Do not forget to assess for silent aspiration: In patients with concurrent swallowing difficulties, as taste changes may indicate broader neurological dysfunction 5