Which thyroid hormone preparations are gluten‑free?

Gluten-Free Thyroid Hormone Preparations

Synthroid (levothyroxine sodium tablets) is confirmed gluten-free, with gluten levels below the FDA detection threshold of 3.0 ppm in all tested formulations. 1

Tablet Formulations

• Synthroid tablets are definitively gluten-free, with laboratory testing demonstrating gluten concentrations below the lowest limit of detection (<3.0 ppm) in both the active pharmaceutical ingredient and all excipients across all tablet strengths 1
• This meets the FDA definition for gluten-free food products, making Synthroid tablets safe for patients with celiac disease or gluten sensitivity 1

Liquid Formulations

• Levothyroxine oral solution (Tirosint-SOL) is gluten-free and lactose-free, making it particularly advantageous for patients with celiac disease who may have impaired absorption with tablet formulations 2, 3
• Switching from tablets to liquid levothyroxine formulation can significantly improve malabsorptive symptoms and thyroid control in patients with celiac disease without requiring dose increases 2
• The liquid formulation demonstrates superior bioavailability in patients with absorption issues, including those with celiac disease, and eliminates concerns about gluten-containing excipients 3, 4

Softgel Formulations

• Softgel levothyroxine preparations (such as Tirosint) are gluten-free and offer enhanced bioavailability compared to tablets, particularly beneficial for patients with celiac disease or malabsorption 4, 5
• These formulations can improve levothyroxine absorption and symptom control in patients who continue to have elevated TSH despite appropriate tablet dosing 4, 5

Clinical Considerations for Celiac Disease

• Celiac disease significantly impairs levothyroxine absorption through intestinal damage, and patients may require 25-50% higher doses when using tablet formulations compared to liquid or softgel preparations 4
• Implementing a gluten-free diet combined with switching to liquid or softgel levothyroxine formulations provides optimal thyroid control in patients with both hypothyroidism and celiac disease 2, 4
• Even after initiating a gluten-free diet, some patients with celiac disease continue to require high levothyroxine doses when using tablets, making liquid or softgel formulations the preferred choice 4

Natural Desiccated Thyroid

• Patients intolerant of gluten who are taking natural desiccated thyroid and still experiencing hypothyroid symptoms can successfully switch to liquid levothyroxine formulations with good tolerability and improved thyroid function 3

Important Caveats

• While Synthroid tablets are gluten-free, they do contain small amounts of aluminum (19-137 µg per tablet depending on strength), though these levels are well below the FDA minimal risk level for chronic oral aluminum exposure 1
• Biotin does not interfere with levothyroxine absorption or metabolism, but it can cause false thyroid function test results through laboratory assay interference; patients should discontinue biotin 2-3 days before thyroid testing 6