What causes a metallic taste?

Causes of Metallic Taste

Metallic taste is most commonly caused by medications (particularly certain antibiotics, antihypertensives, and sleep medications), followed by mineral deficiencies (especially zinc and iron), oral conditions (candidiasis, xerostomia, dental materials), and less commonly by neurological disorders or systemic diseases.

Medication-Induced Metallic Taste

The most frequent culprit in clinical practice is medication-related dysgeusia:

Sleep Medications

• Zopiclone and eszopiclone consistently cause bitter/metallic taste in 7-26% of patients, representing the most common adverse effect of these agents 1
• Risk difference of +0.07 for unpleasant taste compared to placebo, with some studies reporting rates as high as 26.1% versus 5.6% with placebo 2, 1
• This is dose-related and generally not serious enough to preclude use in appropriate patients 1

Tuberculosis Medications

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

Other Medications

• Botulinum toxin A has been reported to cause self-limited metallic taste, possibly through alteration in zinc metabolism 3
• Drug-induced dysgeusia typically improves completely within 2 months after cessation 4

Nutritional Deficiencies

Iron Deficiency

• Iron deficiency is a well-established cause of hypogeusia (decreased taste sensation) 4
• Seven of 25 patients with decreased taste sensation had iron deficiency as the identified cause 4
• Decreased serum iron levels were observed in these patients, and taste thresholds improved with iron repletion 4

Zinc Deficiency

• Zinc deficiency is frequently cited as a cause of metallic taste 5, 6
• However, one study found no decreased serum zinc levels in patients with taste abnormalities, suggesting zinc deficiency may be overemphasized 4

Copper

• Copper overload can cause metallic taste, as demonstrated in a case of a copper-containing foreign body in the gastric wall 7
• Copper deficiency itself is not typically associated with metallic taste 4

Oral and Dental Causes

Dental Materials

• Nickel-containing dental alloys can cause metallic taste through solubility in saliva 5
• The frequency of metal taste correlates with nickel solubility in saliva 5
• Metal hypersensitivity to nickel, aluminum, vanadium, and titanium in dental or orthopedic implants can cause local and systemic symptoms including metallic taste 2

Oral Candidiasis

• Oral candidiasis was identified as the cause in 6 of 25 patients with hypogeusia and 3 of 14 patients with dysgeusia 4
• Treatment of candidiasis typically improves taste symptoms 4

Xerostomia (Dry Mouth)

• Hyposalivation was identified in 6 patients with hypogeusia and 1 patient with dysgeusia 4
• Reduced salivary flow rates contribute to taste disturbances 4

Neurological and Psychiatric Causes

Neuropathic Disorders

• Burning mouth syndrome (BMS) patients frequently report persistently altered metallic taste 6
• BMS is now considered a disorder of altered sensory processing following small fiber neuropathic changes in the tongue 6
• Tongue biopsies show significantly lower density of epithelial nerve fibers in BMS patients 6
• Quantitative assessment reveals significantly higher sensory thresholds in BMS patients compared to controls 6

Psychiatric Distress

• Psychiatric distress was identified as the cause in 3 patients with hypogeusia and 8 patients with dysgeusia 4
• These patients typically do not show improvement in taste thresholds even when symptoms improve 4

Age-Related Changes

• Healthy aging contributes to alterations in olfaction and gustatory sensation 2
• Changes in the muscles of mastication and lower salivary flow rates exacerbate taste problems in older adults 2
• Many medications consumed by older adults contribute to taste disturbances 2

Clinical Approach

When evaluating metallic taste, prioritize the following systematic assessment:

1. Medication review - Most likely cause; consider temporal relationship to medication initiation 2, 1
2. Laboratory testing - Check serum iron, and consider zinc if clinically indicated 4
3. Oral examination - Assess for candidiasis, xerostomia, and dental materials 5, 4
4. Psychiatric screening - Particularly if other causes excluded 6, 4

Important caveat: Dysgeusia (abnormal taste including metallic taste) is typically NOT accompanied by elevated taste thresholds on formal testing, unlike hypogeusia (decreased taste), which shows measurable threshold elevation 4. This distinction can help guide diagnosis and prognosis.