Levothyroxine (T4)
Synthetic T4. Absorption is materially reduced by calcium, iron and magnesium, so timing separation is part of the protocol.
Medications & hormones
Research records
Historical source snapshot. Not freshly verified, not a recommendation. Study findings, community accounts and app defaults are not interchangeable.
Publication suitability · 2026-10-15: Historical reference only; not a clinical verification. Clinical, regulatory, efficacy, safety and dose claims are not independently established by this review.
Levothyroxine (T4)
Synthetic T4. Absorption is materially reduced by calcium, iron and magnesium, so timing separation is part of the protocol.
Evidence category: Regulator / guideline. This describes the source category, not approval or certainty.
Regulatory statement in source: FDA-approved.
Levothyroxine is synthetic thyroxine (T4). A clinical reference states it is FDA-approved for primary, secondary and tertiary hypothyroidism, and for thyrotropin suppression in well-differentiated thyroid cancer. A systematic review of 63 studies found that food, coffee, soy, fibre and calcium or iron supplements all reduced how much of the drug was absorbed. The same review found morning and bedtime intake equally effective. The interaction evidence is review-level and the authors call parts of it limited.
Benefits reported in the imported source
- Hypothyroidism and for thyrotropin suppression in well-differentiated thyroid cancer.
- It is synthetic thyroxine, replacing the hormone the thyroid would make
Risks and limits
- Food, coffee, soy, fibre and calcium or iron supplements all cut how much is absorbed
- A lower start is advised where cardiac disease is present
- The interaction evidence is review-level, and the authors call parts of it limited
Source bottom line: An approved thyroid hormone replacement whose absorption is reduced by coffee, food and several supplements.
Uncertainty: Reference information only. Not medical advice.
Study protocols — reports, not instructions
people with primary, secondary or tertiary hypothyroidism, and thyrotropin-dependent well-differentiated thyroid cancer, per the US label
- Reported regimen
- a single daily dose, about 1.6 mcg/kg/day for full replacement in adults, on an empty stomach half an hour to an hour before breakfast
- Duration
- ongoing, per the label
- Reported outcome
- The label lists it as replacement therapy in hypothyroidism and as an adjunct to surgery and radioiodine in thyroid cancer, with lower starting doses where cardiac disease is present.
- Source
- Synthroid (levothyroxine sodium) — US label (DailyMed)
Claim provenance
evidence.json#/catalog:hormone:levothyroxine/protocols/0
people taking levothyroxine across 63 studies of food and supplement interactions
- Reported regimen
- review of intake timing and co-ingestion: tablets taken 30-60 minutes before breakfast, morning versus bedtime, with coffee, soy, fibre, calcium or iron
- Duration
- not stated
- Reported outcome
- Coffee lowered serum T4 by 29-36% and a one-hour gap prevented it; calcium and iron reduced absorption; morning and bedtime intake were comparable.
- Source
- Levothyroxine Interactions with Food and Dietary Supplements–A Systematic Review (availability check 2026-10-15: possible access barrier; not independently inspected; HTTP 200)
Claim provenance
evidence.json#/catalog:hormone:levothyroxine/protocols/1
Community and practice descriptions
Accounts of a practice are not evidence of safety or effectiveness. Words such as “standard”, “safe” or “recommended” describe the source account, not verified consensus or this wiki’s advice. Commercial and self-published citations are retained for traceability, not vendor endorsement or independent clinical corroboration.
Unverified imported account — Levothyroxine and Calcium: Timing Guide for Safe Use
An imported authored paraphrase, not a quotation or a recommended protocol.
Review: unverified historical account. The imported wording is preserved for attribution; its full clinical, dosing, efficacy or consensus claims have not been independently established. Unvalidated source account; no validated human dosing population or animal-to-human equivalence is inferred.
Imported wording: A health optimization blog describes the reported protocol where levothyroxine is taken in the morning on an empty stomach, with a minimum 4-hour separation before consuming calcium supplements.
Pharmacokinetic context
Historical half-life estimate: 168 hours. FDA label, Synthroid Population/route context and estimates may differ. This is not a schedule or a verified human dosing rule.
Source references
- Synthroid (levothyroxine sodium) — US label (DailyMed)
- Levothyroxine - StatPearls - NCBI Bookshelf (availability check 2026-10-15: possible access barrier; not independently inspected; HTTP 200)
- Levothyroxine Interactions with Food and Dietary Supplements–A Systematic Review (availability check 2026-10-15: possible access barrier; not independently inspected; HTTP 200)
- EMA: levothyroxine (availability check 2026-10-15: source not retrieved; HTTP 404)
Snapshot provenance
Source ID: catalog:hormone:levothyroxine. Commit: adc7684614f9439b41d91a3312b62e7982c7e20e. Review state: historical-not-reverified. Authored links are retained separately from the canonical evidence links in the public data. App templates/defaults and rejected drafts are archived, not deployed.
Related entries and components
None listed.