Does levothyroxine (T4) contain gluten?

Levothyroxine and Gluten Content

Levothyroxine sodium tablets contain no ingredients made from gluten-containing grains (wheat, barley, or rye) and are considered gluten-free. 1

Evidence on Gluten Content in Levothyroxine

The FDA-approved drug label for levothyroxine sodium tablets explicitly states that they "contain no ingredients made from a gluten-containing grain (wheat, barley, or rye)" 1. This is the most authoritative and definitive source regarding the gluten content of this medication.

Additional research confirms this finding:

• A 2017 study specifically examining Synthroid® (a brand of levothyroxine sodium tablets) found that gluten concentrations were below the lowest limit of detection (<3.0 ppm) for all tested lots of the active pharmaceutical ingredient and excipients 2.
• This level is well below the FDA definition for "gluten-free" food products, which requires less than 20 ppm of gluten.

Why This Matters for Patients with Celiac Disease

This information is particularly important for patients with celiac disease who also require thyroid hormone replacement therapy:

• Celiac disease is more common in patients with hypothyroidism, with a prevalence of 1-16% compared to 0.3-1% in the general population 3.
• Untreated celiac disease can significantly impair levothyroxine absorption, requiring higher doses to maintain a euthyroid state 4.
• After treatment of celiac disease, levothyroxine dosing requirements typically decrease significantly as absorption improves 4.

Potential Concerns with Medication Ingredients

While levothyroxine itself is gluten-free, patients with celiac disease should be aware of potentially problematic ingredients in medications generally:

• Starch is a common ingredient in medications that requires source verification, as it could be derived from wheat 3.
• Other potentially problematic ingredients include dextrimaltose, malt, dextrin, maltodextrin, and sodium starch glycolate 3.

Clinical Implications

For patients with celiac disease who require levothyroxine:

1. Levothyroxine is safe to use from a gluten perspective.
2. Monitor thyroid function tests (TSH, free T4) regularly, especially after initiating treatment for celiac disease, as absorption may improve and dose requirements may decrease 4.
3. If unexplained fluctuations in thyroid function occur despite medication adherence, consider:
   • Potential undiagnosed celiac disease (if not already diagnosed)
   • Poor adherence to gluten-free diet affecting absorption
   • Other gastrointestinal disorders that may affect levothyroxine absorption 5

Practical Recommendations

• When switching between different brands or formulations of levothyroxine, verify the gluten-free status of the new product, as inactive ingredients may vary between manufacturers.
• For patients with both celiac disease and hypothyroidism, consistent timing of levothyroxine administration (typically on an empty stomach, 30-60 minutes before breakfast) is particularly important to ensure optimal absorption.
• Pharmacists can help verify the gluten content of specific levothyroxine formulations when uncertainty exists 6.

By ensuring that levothyroxine therapy is truly gluten-free, patients with celiac disease can safely manage their hypothyroidism without compromising their gluten-free diet requirements.