What causes a metallic taste in the mouth?

Causes of Metallic Taste in the Mouth

Metallic taste results from medications (particularly clarithromycin, ethionamide, and sleep medications), metal hypersensitivity from dental/orthopedic implants, chemotherapy, viral infections, and age-related changes in taste perception. 1

Medication-Induced Metallic Taste

Antibiotics

• Clarithromycin causes metallic taste as one of its most common gastrointestinal toxicities, with this effect being dose and serum-level related. 1
• Adult patients generally cannot tolerate clarithromycin at more than 1,000 mg/day, with elderly patients requiring even lower doses (250-500 mg/day) due to toxicity. 1
• Azithromycin primarily causes diarrhea rather than metallic taste, making clarithromycin the more likely culprit when metallic taste occurs with macrolide antibiotics. 1

Tuberculosis Medications

• Ethionamide commonly causes profound metallic taste along with nausea and vomiting, and symptoms may improve if doses are taken with food or at bedtime. 2, 1

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
• 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. 1

Other Medications

• Trientine (used for Wilson disease) may cause loss of taste, particularly in patients with primary biliary cirrhosis. 1
• Intravenous lidocaine can cause metallic taste along with peri-oral numbness and tinnitus in approximately 6.8% of patients. 2
• Acetazolamide causes dysgeusia in approximately 1 in 18 patients. 3
• Botulinum toxin A has been reported to cause metallic taste, though this is rare and self-limited. 4

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, with approximately 10-15% of the population exhibiting allergy to one or more metals. 2, 1
• Chronic exposure to low concentrations of metal ions or particles from dissolution, corrosion, or wear can induce metal hypersensitivity, with metal wear debris acting as haptens that trigger allergic sensitization. 2
• 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. 2, 1
• The nickel solubility in saliva from dental restorations correlates with the frequency of metallic taste and burning sensations. 5

Chemotherapy-Related Metallic Taste

• Metallic taste is reported by 34-46% of cancer patients experiencing taste changes during systemic therapy, affecting those treated with chemotherapy, concomitant radiotherapy, and targeted therapy. 6
• Women experience metallic taste more often than men during cancer treatment. 6
• The etiology of "metal mouth" in chemotherapy remains poorly understood but may involve phantageusia (a form of taste hallucination), direct effects of chemotherapy drugs, chemotherapy-induced sensitization of TRPV1 receptors, or retronasal olfaction of lipid oxidation products. 7
• Patients experiencing metallic taste also report more frequently being bothered by sour food and that everything tastes bitter. 6

Viral Infections

• Viral infections, particularly COVID-19, can cause taste/smell loss in 59-86% of cases and should be considered as a primary cause of taste disturbance. 3

Age-Related Changes

• Healthy aging contributes to alterations in olfaction and gustatory sensation, with changes in the muscles of mastication and lower salivary flow rates exacerbating taste problems in older adults. 1
• Many medications consumed by older adults contribute to taste disturbances, making polypharmacy a key consideration in elderly patients. 1

Nutritional Deficiencies

• Zinc deficiency is a main cause of metallic taste, as alteration in zinc metabolism may affect taste perception. 5, 4

Clinical Approach to Evaluation

When evaluating metallic taste, prioritize a systematic medication review first, followed by assessment for metal implants, recent viral infections, and nutritional deficiencies. 1

Key Steps:

1. Review all current medications, particularly clarithromycin, ethionamide, sleep medications (zopiclone/eszopiclone), and chemotherapy agents. 1
2. Assess for metal implants (dental restorations, orthopedic prostheses) and consider skin patch tests or lymphocyte transformation tests if hypersensitivity is suspected. 2, 1
3. Screen for recent viral infections, especially COVID-19, which can cause taste loss in the majority of cases. 3
4. Evaluate for zinc deficiency and other nutritional deficiencies that may contribute to dysgeusia. 5
5. Examine oral health status, as dental alloy restorations can release metals into bodily fluids and create metallic taste. 2

Important Caveat:

Do not automatically attribute all metallic taste symptoms to a single cause without investigating alternative etiologies, including medication interactions, underlying medical conditions, and disease progression. 8