What causes a metallic taste?

What Causes Metallic Taste

Metallic taste is most commonly caused by medications (particularly clarithromycin, ethionamide, and zopiclone/eszopiclone), metal hypersensitivity from dental or orthopedic implants, burning mouth syndrome, and age-related changes in taste perception. 1, 2

Medication-Induced Metallic Taste

The most frequent culprits are specific drug classes with well-documented mechanisms:

• Clarithromycin causes metallic taste as one of its most common gastrointestinal toxicities, with this effect being dose and serum-level related—adult patients generally cannot tolerate more than 1,000 mg/day, and elderly patients with low creatinine clearance require even lower doses (250-500 mg/day) due to toxicity 1

• Zopiclone and eszopiclone consistently cause bitter/metallic taste in 7-26% of patients, representing the most common adverse effect of these sleep medications, with a risk difference of +0.07 compared to placebo 1

• Ethionamide commonly causes profound metallic taste along with nausea and vomiting, though symptoms may improve if doses are taken with food or at bedtime 1

• Intravenous lidocaine causes metallic taste along with peri-oral numbness and tinnitus in approximately 6.8% of patients 1

• Trientine (used for Wilson disease) may cause loss of taste, particularly in patients with primary biliary cirrhosis 1

• Cancer patients treated with chemotherapy, targeted therapy, or concomitant radiotherapy experience metallic taste in approximately 29% of cases, with women experiencing it more frequently than men 3, 4

Metal Hypersensitivity from Implants and Dental Work

This represents a critical and often overlooked cause:

• Metal hypersensitivity to nickel, aluminum, vanadium, and titanium in dental or orthopedic implants can cause both local and systemic symptoms including metallic taste, affecting approximately 10-15% of the population 1, 5

• Dental alloy restorations can release metals (including lead and cadmium) into saliva, creating persistent metallic taste 2

• The mechanism involves Type IV delayed hypersensitivity reactions where metal wear debris acts as haptens, triggering allergic sensitization 5

• Pre-implantation screening via skin patch tests or lymphocyte transformation tests is recommended for patients with history of metal intolerance to jewelry, belt buckles, watches, or prior metal implants 1, 5

• Metal-on-metal hip prostheses carry higher risk compared to metal-on-polyethylene systems 5

Burning Mouth Syndrome (BMS)

For patients without medication exposure or metal implants:

• Burning mouth syndrome is the most common cause of persistent metallic taste without medication exposure, characterized by burning sensations of the tongue and oral mucosa with altered (metallic) taste or diminished taste sensations 2

• The critical diagnostic feature is normal-appearing oral mucosa—BMS is diagnosed specifically by the absence of visible abnormalities, and normal mucosa should not be dismissed as excluding pathology 2

• Alpha-lipoic acid 200-600 mg daily in divided doses is first-line treatment, with cognitive behavioral therapy as a beneficial adjunct 2

Age-Related Changes

• Healthy aging contributes to alterations in olfaction and gustatory sensation, with changes in muscles of mastication and lower salivary flow rates exacerbating taste problems in older adults 1, 2

• Studies show that taste and smell loss is greatest in older individuals consuming the largest number of prescription drugs 6

Nutritional and Metabolic Causes

• Excess iodine from topical disinfectants, iodinated contrast agents, or environmental chemicals causes metallic taste as a cardinal symptom—measure 24-hour urinary iodine excretion combined with thyroid function tests (TSH, free T4) for diagnostic evaluation 2

• Zinc deficiency can cause metallic taste and altered taste perception 7

Clinical Approach to Evaluation

When evaluating metallic taste, follow this systematic algorithm:

1. Medication review: Identify all current medications, particularly clarithromycin, zopiclone/eszopiclone, ethionamide, chemotherapy agents, and recent medication changes 1

2. Oral examination: Document all dental restorations, implants, recent dental work, and assess for normal-appearing mucosa (suggesting BMS) versus visible pathology 2

3. Exposure history: Ask specifically about intolerance to jewelry, belt buckles, watches, or prior metal implants 1, 5

4. Laboratory testing: Consider serum zinc, 24-hour urinary iodine, thyroid function tests, and serum copper/ceruloplasmin if Wilson's disease suspected 2

5. Patch testing: For patients with metal implants and suspected hypersensitivity, skin patch tests or lymphocyte transformation tests are indicated 1

Critical Pitfalls to Avoid

• Do not prematurely attribute metallic taste to psychiatric causes without ruling out nutritional deficiencies, metal exposure, and iodine toxicity 2

• Do not dismiss normal-appearing oral mucosa as excluding pathology—this is the hallmark of BMS 2

• For patients with metal-on-metal hip implants, routine long-term follow-up every 1-2 years is required due to risk of adverse reactions to metal debris 5

• Blood contamination from periodontitis can cause metallic taste and should be assessed during oral examination 2