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medication

Levothyroxine Sodium

Also known as: Synthroid, Levoxyl

Evidence: High · 100%
Chemical structure of Levothyroxine Sodium (PubChem CID 23666112)
Structure via PubChem
Half-life
168 h
Typical timing
morning
Food rule
empty stomach
Default unit
mcg

Studied for

Longevity

Overview

Levothyroxine sodium is a synthetic thyroid hormone (T4, or L-thyroxine) identical to the hormone naturally produced by the thyroid gland. It is primarily used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. This deficiency can lead to a range of symptoms including fatigue, weight gain, constipation, dry skin, and depression. Levothyroxine works by replacing the missing thyroid hormone, thereby restoring normal metabolic function. It can also be used to treat or prevent certain types of goiter (enlarged thyroid gland) and is sometimes used in conjunction with surgery and radioactive iodine therapy to manage thyroid cancer. Levothyroxine is available as an oral tablet and is typically taken once daily. The synthetic hormone is absorbed from the gastrointestinal tract and then converted to its active form, triiodothyronine (T3), in the body's tissues. This conversion allows it to exert its physiological effects. Because it replaces a naturally occurring hormone, the goal of levothyroxine therapy is to normalize thyroid hormone levels in the blood, alleviating symptoms and preventing long-term complications of hypothyroidism. Regular blood tests are necessary to monitor thyroid-stimulating hormone (TSH) levels, which guide dose adjustments to ensure optimal treatment. (NIH ODS)

Deep dive

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Known interactions

  • 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

Frequently asked

Sources referenced

["DrugBank: Levothyroxine", "EMA SmPC (Summary of Product Characteristics): Levothyroxine", "FDA label: SYNTHROID (levothyroxine sodium) tablets", "Mayo Clinic: Levothyroxine (Oral Route)", "MedlinePlus: Levothyroxine", "NIH ODS (National Institutes of Health Office of Dietary Supplements): Thyroid Hormone", "Cochrane Database of Systematic Reviews: Thyroid hormone therapy for subclinical hypothyroidism in euthyroid adults"]

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 Sodium — Overview, Benefits & Side Effects. Retrieved from https://doseroutine.com/library/levothyroxine-sodium
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