What can cause a metallic taste as a side effect?

Medications and Conditions That Cause Metallic Taste

Metallic taste is most commonly caused by medications, particularly macrolide antibiotics (clarithromycin), sleep medications (eszopiclone/zopiclone), metronidazole, lithium, and anti-tuberculosis drugs (ethionamide), with non-medication causes including metal hypersensitivity from dental implants, burning mouth syndrome, and age-related changes in taste perception.

Medication-Induced Metallic Taste

Macrolide Antibiotics

• Clarithromycin causes metallic taste as one of its most common gastrointestinal toxicities, along with nausea and vomiting, and this effect is dose and serum-level related 1
• Adult patients generally cannot tolerate clarithromycin at more than 1,000 mg/day, with elderly patients with low creatinine clearance or body weight requiring even lower doses (250-500 mg/day) due to toxicity 1
• Azithromycin also causes gastrointestinal symptoms but primarily manifests as diarrhea rather than metallic taste 1

Sleep Medications

• Eszopiclone and zopiclone consistently cause bitter/metallic taste in 7-26% of patients, representing the most common adverse effect of these agents 2
• The risk difference of unpleasant taste compared to placebo is +0.07, with some studies reporting rates as high as 26.1% versus 5.6% with placebo 2

Metronidazole

• The FDA label explicitly states that "a sharp, unpleasant metallic taste is not unusual" with metronidazole 3
• This metallic taste occurs alongside other gastrointestinal effects including nausea (reported by about 12% of patients), vomiting, and abdominal cramping 3

Lithium

• Lithium can cause metallic taste as a miscellaneous adverse reaction unrelated to dosage 4
• This occurs alongside other taste alterations and may resemble symptoms seen with various lithium-related side effects 4

Anti-Tuberculosis Medications

• Ethionamide commonly causes profound metallic taste along with nausea and vomiting, though symptoms may improve if doses are taken with food or at bedtime 2

Chelating Agents

• Trientine (used for Wilson disease) may cause loss of taste, particularly when used in patients with primary biliary cirrhosis 1
• This effect appears related to copper chelation and potential copper deficiency 1

Other Medications

• Carbonic anhydrase inhibitors (acetazolamide, methazolamide) commonly cause metallic taste as a well-documented adverse effect 5
• Botulinum toxin A has been reported to cause metallic taste in at least one case, though this is rare and self-limited 6
• Antihypertensives, antimicrobials, and antidepressants are associated with taste disturbances, though specific metallic taste incidence varies 7

Non-Medication Causes

Metal Hypersensitivity from Implants

• Metal hypersensitivity to nickel, aluminum, vanadium, and titanium in dental or orthopedic implants can cause both local and systemic symptoms including metallic taste 1, 2
• Approximately 10-15% of the population may exhibit allergy to one or more metals commonly used in implantology 1
• Pre-implantation screening via skin patch tests or lymphocyte transformation tests is recommended for patients with history of metal intolerance 1

Burning Mouth Syndrome (BMS)

• BMS 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 8
• The diagnosis is made specifically by the absence of visible oral abnormalities—normal-appearing mucosa should not be dismissed as excluding pathology 8
• Alpha-lipoic acid 200-600 mg daily in divided doses is first-line treatment for BMS 8
• Cognitive behavioral therapy is beneficial, as reassurance and education are crucial since the condition typically does not worsen 8

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 2, 8
• Many medications consumed by older adults contribute to taste disturbances, compounding age-related effects 2

Iodine Toxicity

• Excess iodine from topical disinfectants, iodinated contrast agents, or environmental chemicals causes metallic taste as a cardinal symptom 8
• Diagnostic evaluation requires measuring 24-hour urinary iodine excretion combined with thyroid function tests (TSH, free T4) 8

Dental Causes

• Dental alloy restorations can release lead and cadmium into saliva, potentially causing metallic taste 8
• Contact dermatitis from nickel exposure in earrings and jewelry is common and can cause local reactions 1

Clinical Approach to Metallic Taste

Systematic Assessment

• Prioritize medication review first, specifically looking for clarithromycin, eszopiclone/zopiclone, metronidazole, lithium, ethionamide, and carbonic anhydrase inhibitors 2
• Document all dental restorations, implants, and recent dental work 8
• Perform detailed oral examination to assess for BMS (normal-appearing mucosa), dental restorations, gum disease, or blood contamination from periodontitis 8

Laboratory Testing

• Consider serum zinc levels, 24-hour urinary iodine, thyroid function tests, and serum copper/ceruloplasmin if Wilson's disease is suspected 8
• For patients with metal implants and suspected hypersensitivity, skin patch tests or lymphocyte transformation tests may be 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 8
• Normal-appearing oral mucosa does not exclude BMS—this diagnosis requires the absence of visible abnormalities 8
• When evaluating patients on losartan or other ARBs reporting metallic taste, consider alternative causes including concurrent medications, renal dysfunction, and oral health issues, as metallic taste is rarely reported with ARBs 5

Cancer Treatment Context

• Metallic taste occurs in approximately 29% of cancer patients undergoing treatment, though the quality of evidence is often low 9
• The specific impact on nutritional status and quality of life requires further evaluation 9