Drug Interaction Report

Levothyroxine and Sodium Bicarbonate: Interaction Details

A pharmacist-reviewed analysis of the Levothyroxine and Sodium Bicarbonate interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Sodium Bicarbonate

Alka-Seltzer® Heartburn Desempacho Neut brand of sodium bicarbonate
+

Levothyroxine

Ermeza Euthyrox Levo-T Levo-T® Levothroid® Levoxyl Levoxyl® Synthroid
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Moderate
Can be significant — usually manageable with monitoring.
How we grade severity & evidence

Severity levels

  • Contraindicated: These should generally not be used together.
  • Major: Potentially serious — often needs a change or close monitoring.
  • Moderate: Can be significant — usually manageable with monitoring.
  • Minor: Usually limited clinical impact.

Evidence grades

  • Established: Well documented — supported by controlled studies or strong clinical data.
  • Probable: Good supporting evidence, though not definitively proven.
  • Suspected: Some evidence suggests this interaction, but it is not well established.
  • Possible: Limited or conflicting evidence; the interaction may occur.
  • Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 214 documented Levothyroxine interactions, 196 are rated moderate — including this one.
Onset
rapid
Evidence
probable
Severity
Moderate

What happens

Reduced efficacy of levothyroxine

Interaction Deep Dive

Antacids may cause hypochlorhydria, affect intragastric pH, and reduce levothyroxine absorption32. Concomitant administration of levothyroxine and aluminum- or magnesium-containing antacids may decrease the effect of levothyroxine and increase serum TSH levels 5, potentially resulting in hypothyroidism. If concurrent use is necessary, monitor patients appropriately 32 and adjust levothyroxine dose if necessary 4. Consider administering levothyroxine at least 4 hours before aluminum hydroxide- or magnesium hydroxide-containing products 1.

Why it happens (mechanism)

Reduced levothyroxine absorption

Literature reports

1 report — tap to read

a) The administration of an antacid (containing aluminum and magnesium hydroxide and simethicone) has increased theTSH level in a previously euthyroid patient receiving exogenous levothyroxine. At the end of a 4-month antacid study, a thyroid function test revealed an elevated TSH level. Within 2 weeks following discontinuation of antacid therapy, the serum TSH level decreased. Upon two rechallenges, an elevation in the TSH level recurred despite a delay of 3 hours between administration times of the two agents. The patient remained asymptomatic throughout the course of events. Serum TSH levels should be monitored closely in patients receiving levothyroxine and antacids containing aluminum and magnesium hydroxide or simethicone 5.

Common questions

Can I take Levothyroxine and Sodium Bicarbonate together?

Reduced efficacy of levothyroxine Always confirm with your pharmacist or prescriber before making any change.

How serious is the Levothyroxine and Sodium Bicarbonate interaction?

It is rated moderate. Can be significant — usually manageable with monitoring.

How quickly could this interaction happen?

The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.

How strong is the evidence for this interaction?

The evidence is graded "probable". Good supporting evidence, though not definitively proven.

Questions for your pharmacist

  • Does my dose of Levothyroxine or Sodium Bicarbonate need adjusting while I take them together?
  • What symptoms should prompt me to call you or my prescriber right away?
  • Does the timing of my doses matter for this combination?
  • Is there anything you'd monitor while I'm on both?

References (5)

  1. Centanni M, Duntas L, Feldt-Rasmussen U, et al: ETA guidelines for the use of levothyroxine sodium preparations in monotherapy to optimize the treatment of hypothyroidism. Eur Thyroid J 2025; 14(4):e250123. PubMed
  2. Product Information: TIROSINT(R)-SOL oral solution, levothyroxine sodium oral solution. IBSA Pharma Inc. (per FDA), Parsippany, NJ, 2023. DailyMed
  3. Product Information: SYNTHROID(R) oral tablets, levothyroxine sodium oral tablets. AbbVie Inc (per FDA), North Chicago, IL, 2022. DailyMed
  4. Liu H, Lu M, Hu J, et al: Medications and food interfering with the bioavailability of levothyroxine: a systematic review. Ther Clin Risk Manag 2023; 19:503-523. DOI
  5. Sperber AD & Liel Y: Evidence for interference with the intestinal absorption of levothyroxine sodium by aluminum hydroxide. Arch Intern Med 1992; 152:183-184. DOI
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Sodium Bicarbonate

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Levothyroxine

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Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Levothyroxine + Activated Charcoal Tiratricol Acetyl-l-carnitine Alpha-lipoic Acid Ascophyllum Nodosum Ashwagandha Bugleweed Calcium + 42 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.