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Thyroid Hormone Replacement

Levothyroxine

Also sold as Synthroid

Absorption is reduced by calcium, iron, and food; separate dosing by at least 4 hours.

This page provides educational information about possible medication-related nutrient relationships. It does not diagnose a deficiency, establish that this medication caused a symptom, or replace qualified medical care.
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Overview

About Levothyroxine

Levothyroxine belongs to the Thyroid Hormone Replacement class. Recognized brand names include Synthroid.

Absorption is reduced by calcium, iron, and food; separate dosing by at least 4 hours.

MyDeficiencies does not provide dosing instructions, adverse-effect lists, or personalized medical advice. Always follow the guidance of your prescribing clinician and pharmacist.

Nutrient relationships

Possible Nutrient Relationships

  • Iron

    Emerging Evidence

    Required for thyroid peroxidase and oxygen transport.

    Available evidence suggests Levothyroxine may affect iron status. Individual responses vary.

  • Calcium

    Emerging Evidence

    Bone health and signaling.

    Available evidence suggests Levothyroxine may affect calcium status. Individual responses vary.

How to read this page

Evidence Strength

Evidence labels reflect the current strength of available research, not a guarantee of individual outcomes:

  • Stronger Evidence — Consistent, replicated evidence across multiple well-designed studies.
  • Moderate Evidence — Supportive evidence with some variability across populations or study designs.
  • Emerging Evidence — Early or mechanistic signals that warrant continued study.

Read our full evidence framework →

Proposed mechanisms

How These Relationships May Occur

Absorption is impaired by divalent cations (calcium, iron) and food matrix interactions; thyroid hormone activity drives mitochondrial throughput.

A proposed mechanism explains how a relationship might occur. It does not prove that a clinically meaningful deficiency occurs in every individual.

Body systems

Body Systems That May Be Relevant

  • Oxygen & ATP

    Emerging Evidence

    Oxygen delivery and cellular energy metabolism may be relevant.

Combinations reviewed

Reviewed Combinations

  • Levothyroxine + Omeprazole

    Moderate Evidence

    PPI-induced hypochlorhydria reduces levothyroxine dissolution and absorption.

    May cause sub-therapeutic thyroid hormone levels and recurrent hypothyroid symptoms.

For your next visit

Questions You May Want to Discuss

  • Could Levothyroxine affect any nutrients over time in my situation?
  • Are there symptoms or risk factors that would make further evaluation appropriate?
  • Could diet, other medications, or health conditions affect this relationship?
  • Would laboratory testing be clinically appropriate for me?
  • Are there medication or supplement interactions I should understand?

These are conversation starters, not recommendations to request a specific test, supplement, or medication change.

Research

Research and Sources

Formal citations for Levothyroxine are being catalogued. See our Research Center for evidence standards and methodology.

See our evidence methodology for how sources are evaluated.

View MyDeficiencies research updates(research revisions are tracked centrally, including for Levothyroxine)
Related nutrients

Related Nutrients

  • Iron
    Emerging Evidence
  • Calcium
    Emerging Evidence
Ready to go deeper

Explore Levothyroxine in Your Report

Add Levothyroxine to a MyDeficiencies analysis to view its reviewed nutrient relationships alongside other medications, supplements, symptoms, and relevant context.

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Educational only. Not a diagnosis. Not a substitute for qualified medical care.