DoseRoutineDoseRoutine
medicationControlled

Levothyroxine

Also known as: synthroid

Evidence: High · 100%
Chemical structure of Levothyroxine (PubChem CID 5819)
Structure via PubChem
Half-life
—
Typical timing
morning
Food rule
empty stomach
Default unit
mcg

Studied for

Longevity

Overview

Levothyroxine, also known by brand names like Synthroid, is a synthetic form of the thyroid hormone thyroxine (T4). It is primarily used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormones. Thyroid hormones are crucial for regulating the body's metabolism, growth, and development. When the body lacks sufficient thyroid hormones, various bodily functions can slow down, leading to symptoms like fatigue, weight gain, constipation, and cold intolerance. Levothyroxine works by replacing the missing hormone, restoring normal metabolic function. Levothyroxine is also used to treat or prevent various types of goiter (enlargement of the thyroid gland) and, in conjunction with surgery and radioactive iodine therapy, to manage thyroid cancer. It is a prescription medication and its use must be directed and monitored by a licensed clinician. (NIH ODS)

Deep dive

Tap a section to expand.

Known interactions

  • Compound-pair rule
    Caution

    Calcium reduces absorption of thyroid medication when taken together.

    Separate by about 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Iron reduces absorption of thyroid medication when taken together.

    Separate by about 4 hours.

    Suggested separation: 4 h

  • Category rule: supplement × medication
    Note

    Some supplements change how the body processes medications (absorption, liver enzymes, or additive effects).

    Specific pairs are checked against a licensed drug database and shown with their own severity. Always confirm with your provider or pharmacist.

  • Category rule: vitamin × medication
    Note

    Certain vitamins interact with specific medications (e.g., vitamin K with blood thinners).

    Specific pairs are checked against a licensed source; confirm with your provider.

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Divalent cations chelate levothyroxine in the gut and reduce absorption by up to 30%.

    Take levothyroxine on empty stomach; separate mineral supplements by at least 4 hours.

    Suggested separation: 4 h

  • Compound-pair rule
    Caution

    Reduced gastric acid impairs levothyroxine absorption.

    Monitor TSH after starting/stopping PPI; dose adjustment may be needed.

  • Compound-pair rule
    Caution

    Reduced gastric acid impairs levothyroxine absorption.

    Monitor TSH after starting/stopping PPI; dose adjustment may be needed.

  • Compound-pair rule
    Caution

    Reduced gastric acid impairs levothyroxine absorption.

    Monitor TSH after starting/stopping PPI; dose adjustment may be needed.

  • Compound-pair rule
    Caution

    Reduced gastric acid impairs levothyroxine absorption.

    Monitor TSH after starting/stopping PPI; dose adjustment may be needed.

  • Compound-pair rule
    Caution

    Reduced gastric acid impairs levothyroxine absorption.

    Monitor TSH after starting/stopping PPI; dose adjustment may be needed.

  • Compound-pair rule
    Note

    Ashwagandha can raise T4/T3 levels and may amplify thyroid medication effect.

    Monitor TSH when starting ashwagandha on levothyroxine.

  • Compound-pair rule
    Note

    May raise thyroid hormone; can amplify levothyroxine effect.

    Monitor TSH when combining.

Frequently asked

Sources referenced

["NIH ODS (National Institutes of Health Office of Dietary Supplements)", "MedlinePlus (National Library of Medicine)", "PubChem (National Library of Medicine)", "Mayo Clinic", "FDA label (U.S. Food and Drug Administration)", "EMA SmPC (European Medicines Agency Summary of Product Characteristics)", "Cochrane Library", "DrugBank"]

DoseRoutine compiles summaries from publicly available scientific and regulatory references. Always verify important decisions with a licensed clinician.

Cite this page

Using this in an article, AI answer, or research note? Please attribute:

DoseRoutine. (2026). Levothyroxine — Overview, Benefits & Side Effects. Retrieved from https://doseroutine.com/library/levothyroxine
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