Drug & supplement interaction

Thyroid Extract + Bismuth Subsalicylate (OTC drug)

Bismuth Subsalicylate (OTC drug) brand names: Pepto-Bismol, Kaopectate Anti-Diarrheal Caplets (U.S.), Maalox Total Stomach Relief, Maalox Multi Action, Kaopectate Liquid (U.S.), and others.

Minor Interaction
Medically reviewed by · Updated November 2023
The bottom line Minor

Thyroid Extract has a minor interaction with Bismuth Subsalicylate (OTC drug). Food and medications can interfere with thyroid hormone absorption.

Read the full interaction report
SeverityMinor
LikelihoodLikely
EvidenceA
What do Severity, Likelihood & Evidence mean?
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Interaction report

Thyroid Extract and Bismuth Subsalicylate (OTC drug)

Here is the interaction we found between these two, with the evidence behind it.

Minor

Oral Drugs

Why this applies to Bismuth Subsalicylate (OTC drug)

Bismuth Subsalicylate (OTC drug) falls under Oral Drugs — the group Thyroid Extract interacts with.

Food and medications can interfere with thyroid hormone absorption. Some foods, particularly those high in fiber or containing certain minerals like calcium or iron, can bind to thyroid hormones and reduce their absorption in the digestive tract. Additionally, taking thyroid medications with certain drugs, like antacids or calcium supplements, can hinder the effectiveness of the thyroid medication, necessitating adjustments in dosage or timing. Prescription thyroid medications, such as Synthroid, are recommended to be taken on an empty stomach, at least 30 minutes before food and other medications, for optimal absorption.
Severity Minor Likelihood Likely Evidence A

Well-controlled human studies have demonstrated the likely existence of this interaction.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the simple version: Pepto-Bismol and similar bismuth products can act a bit like an antacid in your stomach, and that's where the overlap with thyroid extract comes in. When the two share the same window of time, the bismuth can bind up the thyroid hormone (the T4 and T3 in the extract) so your body absorbs less of it. The result isn't a dangerous reaction, just a weaker dose of thyroid, which over time could mean lingering tiredness, feeling cold, or sluggishness if it happens regularly.

The easy fix is timing. Take your thyroid extract on an empty stomach, then wait several hours before reaching for the bismuth. Occasional use for an upset stomach is unlikely to matter much. If you rely on both often, check with your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Thyroid Extract Also Interacts With Other Medications

Thyroid Extract has 3 moderate, 2,018 minor known drug interactions in our database — the Bismuth Subsalicylate (OTC drug) one above is one of them. If you take anything else, check it against the full list below.

Moderate 3 Minor 2,018 No known interaction 809 (incl. Bismuth Subsalicylate (OTC drug))
Taking anything else?

Check Another of Your Medications Against Thyroid Extract

Covers the 2,830 medications we’ve checked against Thyroid Extract. Pick one to open its full report.

From our Q&A

Questions About Thyroid Extract or Bismuth Subsalicylate (OTC drug)

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Thyroid Extract or Bismuth Subsalicylate (OTC drug), not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Bismuth Subsalicylate (OTC drug)

This page covers Thyroid Extract only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Bismuth Subsalicylate (OTC drug) page lists 17 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Coffee Charcoal (moderate), European Mandrake (moderate), Glucomannan (moderate) and Guar Gum (moderate).

By severity: 1 major · 7 moderate · 9 minor.

From our pharmacist’s overview on the Bismuth Subsalicylate (OTC drug) page

“Everything on this page interacts with bismuth subsalicylate (Pepto-Bismol, Kaopectate) the same basic way, by changing how much of the medicine your gut actually absorbs, and one entry deserves genuine caution. Activated charcoal, the only major-rated interaction of the 17, is another stomach remedy people often take at the same time,…”

Reviewed by 2 · Jul 18, 2026

Open the Bismuth Subsalicylate (OTC drug) interaction page

How much people look this up

Where Thyroid Extract and Bismuth Subsalicylate (OTC drug) Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Thyroid Extract
Top half

#601 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Bismuth Subsalicylate (OTC drug)
Top 25%

#693 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Thyroid Extract

What is Thyroid Extract?

Thyroid Extract
  • Hypothyroidism (underactive thyroid)
  • Fatigue and low energy
  • Weight management
  • Sluggish metabolism
  • General thyroid support

Thyroid extract supplements are made from dried animal thyroid gland and may contain real thyroid hormones (T3 and T4), but the amounts in over-the-counter products are not standardized and can be unpredictable. Self-treating a thyroid problem with these supplements can be risky, so always work with a doctor or pharmacist and use prescription thyroid medicine when treatment is needed.

Read the full Thyroid Extract monograph & all interactions
Medication

About Bismuth Subsalicylate

What Is Bismuth Subsalicylate Used For?

Brand names: Pepto-Bismol, Kaopectate Anti-Diarrheal Caplets (U.S.), Maalox Total Stomach Relief, Maalox Multi Action, Kaopectate Liquid (U.S.), Kaopectate Extra Strength Liquid (U.S.)

Bismuth subsalicylate relieves a wide range of digestive complaints. Across all supported products, it is used for diarrhea, traveler's diarrhea, and upset stomach caused by overindulgence in food and drink.

Specific symptoms it targets include:

  • Heartburn
  • Indigestion
  • Nausea
  • Gas
  • Belching
  • Fullness

See full Bismuth Subsalicylate drug information
Keep checking

Other Drugs & Thyroid Extract

Browse every other medication we’ve checked against Thyroid Extract — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
3Moderate
2,018Minor
808No known interaction
3 Moderate 2,018 Minor 808 No interaction
Moderate

3 interactions

Minor

2,018 interactions

Showing 60 of 2,018 minor interactions — see all 2,018 on the Thyroid Extract page.

No interaction 808 drugs checked — show the list

We also checked Thyroid Extract against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 808 medications checked with no known interaction — see the full Thyroid Extract list.

See the full Thyroid Extract interactions page
See every supplement checked against Bismuth Subsalicylate (OTC drug), ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Thyroid Extract monograph › Uses, safety, and every drug interaction in one place Bismuth Subsalicylate (OTC drug) supplement interactions › Every supplement checked against Bismuth Subsalicylate (OTC drug), ranked by severity Bismuth Subsalicylate drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Thyroid Extract and Bismuth Subsalicylate (OTC drug) Together: Common Questions

Can you take Thyroid Extract with Bismuth Subsalicylate (OTC drug)?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Thyroid Extract and Bismuth Subsalicylate (OTC drug) interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Bismuth Subsalicylate (OTC drug) and Thyroid Extract?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.