Can iron supplements cause a black film on the tongue?

Black Film on Tongue from Iron Tablets

Yes, iron tablets can cause a black film or discoloration on the tongue, which is a recognized side effect of oral iron supplementation. This discoloration is specifically mentioned in clinical guidelines as one of the potential oral cavity side effects of iron therapy.

Mechanism and Evidence

According to the American Academy of Dermatology guidelines, oral cavity discoloration (including tongue, lip, and gum) is a documented adverse effect of certain medications, including iron supplements 1. This occurs because:

• Iron can interact with sulfur-containing proteins in saliva
• Unabsorbed iron can deposit on the surface of the tongue
• The reaction between iron and oral bacteria can create visible discoloration

Types of Iron Supplements and Their Effects

Different iron formulations have varying propensities to cause oral discoloration:

1. Ferrous Sulfate: Most commonly associated with tongue discoloration

   • Contains 65mg elemental iron per 200mg tablet 1
   • Has higher incidence of overall side effects (32.3%) compared to other formulations 2

2. Ferrous Fumarate: Also associated with oral side effects

   • Contains 69-106mg elemental iron per tablet 1
   • Has the highest rate of gastrointestinal adverse effects (43.4%) among iron supplements 2

3. Ferric Maltol: Newer formulation with potentially fewer side effects 3

Management of Tongue Discoloration

If a patient experiences black film on the tongue from iron tablets:

1. Reassure the patient: This is a harmless cosmetic side effect and not a sign of toxicity

2. Oral hygiene measures:

   • Regular gentle brushing of the tongue
   • Rinsing mouth thoroughly after taking iron supplements
   • Using a tongue scraper carefully

3. Consider alternative formulations:

   • Switch to a different iron salt (e.g., from sulfate to gluconate)
   • Try liquid formulations which may cause less direct contact with the tongue
   • Extended-release ferrous sulfate with mucoproteose has the lowest incidence of adverse effects (4.1%) 2

4. Dosing modifications:

   • Alternate-day dosing may improve absorption and reduce side effects 4
   • Taking iron with vitamin C can enhance absorption, potentially allowing lower doses 4

Other Common Side Effects of Iron Supplements

Besides tongue discoloration, patients should be aware of:

• Gastrointestinal effects: nausea, constipation, diarrhea, abdominal pain
• Stool discoloration (black or dark green)
• Tooth staining with liquid preparations
• Rare but severe: oral mucosal ulceration 5

When to Consider Alternative Iron Delivery Methods

If oral side effects are intolerable:

• Consider intravenous iron therapy for patients with severe intolerance to oral preparations 4
• IV iron is specifically indicated for patients with inflammatory bowel disease, chronic kidney disease, or heart failure who cannot tolerate oral iron 4

The black film on the tongue from iron tablets is generally harmless and resolves when the medication is discontinued or with improved oral hygiene practices. If the discoloration is particularly bothersome, switching to a different iron formulation may help while still addressing the underlying iron deficiency.