Drug & supplement interaction

Bifidobacterium Longum + Levothyroxine

Levothyroxine brand names: Euthyrox, Levothroid, Unithroid, Synthroid, Levoxyl, and others.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Bifidobacterium Longum and Levothyroxine in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the label for Levothyroxine states a food rule worth keeping to.

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Interaction report

Bifidobacterium Longum and Levothyroxine

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Levothyroxine and Bifidobacterium Longum in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Bifidobacterium Longum safety at a glance

Bifidobacterium Lo... overall Use caution Generally well tolerated in healthy people, but caution is needed for those who are seriously ill or immune-compromised.
Pregnancy Possibly Safe When used orally and appropriately, short-term. A combination of Bifidobacterium longum and Lacticaseibacillus rhamnosus has been used with apparent safety thro... Read the full pregnancy detail
Breastfeeding Possibly Safe When used orally and appropriately, short-term. A combination of Bifidobacterium longum and Lacticaseibacillus rhamnosus has been used with apparent safety thro... Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Levothyroxine and Bifidobacterium Longum? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Levothyroxine

Interactions in our licensed database are recorded against drug classes, not just single drug names. Levothyroxine is filed under 3 classifications — including thyroid hormone, oral drugs. Bifidobacterium Longum has documented interactions with 1 drug class — the most serious being antibiotic drugs (moderate) — and none of Levothyroxine’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Bifidobacterium Longum Does Interact With Other Medications

Bifidobacterium Longum has 182 moderate known drug interactions in our database — Levothyroxine isn’t one of them. If you take anything else, check it against the full list below.

Moderate 182 No known interaction 2,648 (incl. Levothyroxine)
Taking anything else?

Check Another of Your Medications Against Bifidobacterium Longum

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

What to actually watch for

What Bifidobacterium Longum Itself Has Been Linked To

This is not an interaction — nothing below involves Levothyroxine. It is the side-effect record for Bifidobacterium Longum on its own, from the licensed Natural Medicines monograph. If something new turns up after you add Bifidobacterium Longum, this list is the first place to look. One entry is worth acting on rather than waiting out — marked below.

  • A higher chance of infection Worth acting on Additional detail

    “There have been rare cases of Bifidobacterium bacteremia in critically ill infant and adult patients. Various cases of Bifidobacterium longum bacteremia, sometimes presenting as sepsis, have occurred in preterm infants using probiotics.”

    Bifidobacterium Longum · Natural Medicines adverse-effect record, reported in cancer.

    6 sources cited
    1. 102416. Pruccoli G, Silvestro E, Pace Napoleone C, Aidala E, Garazzino S, Scolfaro C. Are probiotics safe? Bifidobacterium bacteremia in a child with severe heart failure. Infez Med. 2019;27(2):175-178.
    2. 107599. Esaiassen E, Hjerde E, Cavanagh JP, Simonsen GS, Klingenberg C; Norwegian Study Group on Invasive Bifidobacterial Infections. Bifidobacterium bacteremia: Clinical characteristics and a genomic approach to assess pathogenicity. J Clin Microbiol. 2017;55(7) PubMed
    3. 111610. US Food and Drug Administration (FDA). Dear Healthcare Provider Letter: Warning Regarding Use of Probiotics in Preterm Infants. September 2023. Available at: https://www.fda.gov/media/172606/download?attachment. Accessed November 1, 2023.
    4. 111612. Pillai A, Tan J, Paquette V, Panczuk J. Does probiotic bacteremia in premature infants impact clinically relevant outcomes? A case report and updated review of literature. Clin Nutr ESPEN. 2020;39:255-259. PubMed
    5. 111850. Zbinden A, Zbinden R, Berger C, Arlettaz R. Case series of Bifidobacterium longum bacteremia in three preterm infants on probiotic therapy. Neonatology 2015;107(1):56-9.
    6. 111852. Bertelli C, Pillonel T, Torregrossa A, et al. Bifidobacterium longum bacteremia in preterm infants receiving probiotics. Clin Infect Dis 2015;60(6):924-7. PubMed
  • Bloating or gas / Stomach upset / Constipation Additional detail

    “When taken orally, abdominal discomfort, pain, and distension have been reported rarely. Flatulence has been reported rarely with Bifidobacterium longum when used alone or in combination with other species of probiotics. Other rare gastrointestinal side effects have included constipation and gastrointestinal motor disorder.”

    Bifidobacterium Longum · Natural Medicines adverse-effect record, reported in constipation.

    4 sources cited
    1. 111773. Sabaté JM, Iglicki F. Effect of Bifidobacterium longum 35624 on disease severity and quality of life in patients with irritable bowel syndrome. World J Gastroenterol 2022;28(7):732-744.
    2. 111847. Malaguarnera M, Greco F, Barone G, Gargante MP, Malaguarnera M, Toscano MA. Bifidobacterium longum with fructo-oligosaccharide (FOS) treatment in minimal hepatic encephalopathy: a randomized, double-blind, placebo-controlled study. Dig Dis Sci 2007;52(11) PubMed
    3. 111856. Sangkanjanavanich S, Pradubpongsa P, Mitthamsiri W, Sangasapaviliya A, Boonpiyathad T. Bifidobacterium infantis 35624 efficacy in patients with uncontrolled asthma: A randomized placebo-controlled trial. Ann Allergy Asthma Immunol 2022;129(6):790-792. PubMed
    4. 107520. Shahriari A, Karimi E, Shahriari M, Aslani N, Khooshideh M, Arab A. The effect of probiotic supplementation on the risk of gestational diabetes mellitus among high-risk pregnant women: A parallel double-blind, randomized, placebo-controlled clinical trial PubMed
  • Cough Additional detail

    “When taken orally, a dry cough has been reported by a single patient in a clinical trial.”

    Bifidobacterium Longum · Natural Medicines adverse-effect record, reported in cough.

    1 source cited
    1. 111851. Tamaki H, Nakase H, Inoue S, et al. Efficacy of probiotic treatment with Bifidobacterium longum 536 for induction of remission in active ulcerative colitis: A randomized, double-blinded, placebo-controlled multicenter trial. Dig Endosc 2016;28(1):67-74.

Everything above comes from the Natural Medicines adverse-effect record for Bifidobacterium Longum — expand a row for the licensed statement it rests on. We read the ADVERSE REACTIONS section of Levothyroxine’s FDA label too, and the two lists don’t meaningfully overlap — which is why no Levothyroxine column appears here.

Special populations

Bifidobacterium Longum in Pregnancy & Breastfeeding

Pregnancy And Lactation Possibly Safe

When used orally and appropriately, short-term. A combination of Bifidobacterium longum and Lacticaseibacillus rhamnosus has been used with apparent safety throughout pregnancy. A combination of B. longum BB536 and Bifidobacterium breve M-16V has been used with apparent safety from about 4 weeks before the expected due date until delivery. Also, a combination of B. longum and Lacticaseibacillus paracasei has been used with apparent safety from 2 months prior to delivery until 2 months after delivery during lactation.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.© 2026 Therapeutic Research Center

How to take them

Some Levothyroxine Products Have a Food Rule — Bifidobacterium Longum Should Not Break It

At least one FDA label for a product containing Levothyroxine says to take it on an empty stomach. Most supplements — Bifidobacterium Longum included — are taken with a meal, so the easy mistake is swallowing both together at breakfast. Where that rule applies, keep Levothyroxine on its own and move Bifidobacterium Longum to a meal later in the day.

This may not be true of your version. Food instructions belong to the product, not the ingredient: two Levothyroxine products can carry different directions, and extended-release forms often differ from immediate-release ones. The label we read is quoted below — check the directions on your own box or bottle, or ask your pharmacist, for how to take the exact product you were given.

A food rule is not an interaction — it is about how much of the medicine you absorb. The directions that came with your own product, and your pharmacist, outrank anything on this page.

Overlapping uses

What Levothyroxine Is Prescribed For, and What Bifidobacterium Longum Has Been Studied For

These two come up together because they touch the same health topic — not because they do the same job. Levothyroxine is a prescription medicine with approved uses on its FDA label. Bifidobacterium Longum is a supplement: what follows is what researchers have looked at it for, and how strong that evidence is.

Levothyroxine is prescribed for: Levothyroxine replaces or supplements the thyroid hormone your body isn't making enough of. It's used for hypothyroidism — an underactive thyroid — in adults, children, and even newborns, whether the cause is the thyroid gland itself, the pituitary gland, or the hypothalamus in the brain. It's also used alongside surgery and radioiodine treatment in people with certain types of thyroid cancer, to help suppress the hormone that can stimulate cancer growth. It is not meant for weight loss, treating benign thyroid nodules in people who have enough iodine, or for hypothyroidism during recovery from a temporary condition called subacute thyroiditis.

Bifidobacterium Longum has been studied for:

  • Depression studied, not established Bifidobacterium Longum has been studied for this. Natural Medicines rates the evidence: Insufficient Reliable Evidence To Rate Read what the research shows

    Bifidobacterium Longum for depression

    Oral Bifidobacterium longum has only been evaluated in combination with other ingredients; its effect when used alone is unclear.

  • Constipation studied, not established Bifidobacterium Longum has been studied for this. Natural Medicines rates the evidence: Insufficient Reliable Evidence To Rate Read what the research shows

    Bifidobacterium Longum for constipation

    It is unclear if oral Bifidobacterium longum is beneficial for constipation.

Effectiveness ratings and the research summaries above are the verbatim record from the Natural Medicines database, which grades evidence from “Effective” down to “Insufficient Reliable Evidence To Rate”. A rating below the top of that scale means researchers have looked at it — not that it works, and never that it can stand in for a prescribed medicine. Do not stop or replace Levothyroxine on your own; if you are taking Bifidobacterium Longum for the same health topic, tell your prescriber, especially if the medicine is being adjusted to a target.

From our Q&A

Questions About Bifidobacterium Longum or Levothyroxine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Bifidobacterium Longum or Levothyroxine, 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 Levothyroxine

This page covers Bifidobacterium Longum only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Levothyroxine page lists 50 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Tiratricol (major), Acetyl-l-carnitine (moderate), Alpha-lipoic Acid (moderate) and Ascophyllum Nodosum (moderate).

By severity: 2 major · 39 moderate · 9 minor.

From our pharmacist’s overview on the Levothyroxine page

“Levothyroxine replaces a hormone your body measures in tiny amounts, so small shifts in its blood level show up in how you feel, and I treat this list with genuine care. Nearly everything on it does one of two things: blocks the pill from being absorbed in the gut, the way everyday minerals like calcium do by binding it into complexes,…”

Reviewed by 2 · Jul 18, 2026

Open the Levothyroxine interaction page

One more smart check

Taking Bifidobacterium Longum as Part of a Dietary Supplement Product? Check It for Interactions

We hold 3,189 real supplement products containing Bifidobacterium Longum, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Bifidobacterium Longum. Even though Bifidobacterium Longum itself has no known interaction with Levothyroxine, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Bifidobacterium Longum and Levothyroxine 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 Bifidobacterium Longum
Top 10%

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

29 days ago today
Medication Levothyroxine
Top 10

#2 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Bifidobacterium Longum reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Bifidobacterium Longum and Levothyroxine records this page draws on were last updated July 10, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About Bifidobacterium Longum

What is Bifidobacterium Longum?

  • Digestive health and regularity
  • Irritable bowel syndrome (IBS)
  • Diarrhea (including antibiotic-related)
  • Immune support
  • Mood and stress (gut-brain axis)

Bifidobacterium longum is a 'friendly' bacterium found naturally in the human gut and used as a probiotic. It is generally well tolerated and is most studied for digestive issues, though evidence for many uses is still limited or mixed. Talk to your pharmacist or doctor before using it, especially if you have a weakened immune system.

Bifidobacterium longum · Bifidobacteriaceae · Live bacterial cells (probiotic) · Capsules, tablets, powders, sachets, fermented foods, and multi-strain probiotic blends

An interaction check asks whether these two react with each other — it does not ask whether Bifidobacterium Longum is a good idea for someone in your situation. Here is what our Bifidobacterium Longum record says about it on its own.

Bifidobacterium Longum: dosing

There is no single established 'correct' dose for Bifidobacterium longum. Probiotic doses are usually measured in colony-forming units (CFU), and products vary widely in how many CFU they contain and which strains they include.The best approach is to follow the directions on your specific product's label. Keep the product stored as directed (some need refrigeration) to keep the bacteria alive and effective.

From our Bifidobacterium Longum monograph — the full record covers uses, side effects and every documented interaction.

Read the full Bifidobacterium Longum monograph & all interactions
Medication

About Levothyroxine

What Is Levothyroxine Used For?

Brand names: Euthyrox, Levothroid, Unithroid, Synthroid, Levoxyl, Levo-T, Eltroxin, Estre, Levothyroxine, Novothyrox, Levolet

Levothyroxine replaces or supplements the thyroid hormone your body isn't making enough of. It's used for hypothyroidism — an underactive thyroid — in adults, children, and even newborns, whether the cause is the thyroid gland itself, the pituitary gland, or the hypothalamus in the brain.

It's also used alongside surgery and radioiodine treatment in people with certain types of thyroid cancer, to help suppress the hormone that can stimulate cancer growth. It is not meant for weight loss, treating benign thyroid nodules in people who have enough iodine, or for hypothyroidism during recovery from a temporary condition called subacute thyroiditis.

See full Levothyroxine drug information
Keep checking

Other Drugs & Bifidobacterium Longum

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

0Major
182Moderate
0Minor
2,647No known interaction
182 Moderate 2,647 No interaction
Moderate

182 interactions

Showing 60 of 182 moderate interactions — see all 182 on the Bifidobacterium Longum page.

No interaction 2,647 drugs checked — show the list

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

Showing the 60 most looked-up of 2,647 medications checked with no known interaction — see the full Bifidobacterium Longum list.

See the full Bifidobacterium Longum interactions page
See every supplement checked against Levothyroxine, ranked by severity
Evidence & sources

Bifidobacterium Longum References

The 21 references that drive our Bifidobacterium Longum monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Ha GY, Yang CH, Kim H, Chong Y. Case of sepsis caused by Bifidobacterium longum. J Clin Microbiol 1999;37:1227-8.
  2. Pierce A. The American Pharmaceutical Association Practical Guide to Natural Medicines. New York: The Stonesong Press, 1999:19.
  3. Xiao JZ, Takahashi S, Odamaki T, et al. Antibiotic susceptibility of bifidobacterial strains distributed in the Japanese market. Biosci Biotechnol Biochem. 2010;74(2):336-42. PubMed
  4. Rautava S, Kainonen E, Salminen S, Isolauri E. Maternal probiotic supplementation during pregnancy and breast-feeding reduces the risk of eczema in the infant. J Allergy Clin Immunol. 2012;130(6):1355-60. PubMed
  5. Pruccoli G, Silvestro E, Pace Napoleone C, Aidala E, Garazzino S, Scolfaro C. Are probiotics safe? Bifidobacterium bacteremia in a child with severe heart failure. Infez Med. 2019;27(2):175-178.
  6. Pellonperä O, Vahlberg T, Mokkala K, et al. Weight gain and body composition during pregnancy: a randomised pilot trial with probiotics and/or fish oil. Br J Nutr. 2020 Nov 4:1-11. PubMed
  7. Pellonperä O, Mokkala K, Houttu N, et al. Efficacy of fish oil and/or probiotic intervention on the incidence of gestational diabetes mellitus in an at-risk group of overweight and obese women: A randomized, placebo-controlled, double-blind clinical trial PubMed
  8. Shahriari A, Karimi E, Shahriari M, Aslani N, Khooshideh M, Arab A. The effect of probiotic supplementation on the risk of gestational diabetes mellitus among high-risk pregnant women: A parallel double-blind, randomized, placebo-controlled clinical trial PubMed
  9. Esaiassen E, Hjerde E, Cavanagh JP, Simonsen GS, Klingenberg C; Norwegian Study Group on Invasive Bifidobacterial Infections. Bifidobacterium bacteremia: Clinical characteristics and a genomic approach to assess pathogenicity. J Clin Microbiol. 2017;55(7) PubMed
  10. Enomoto T, Sowa M, Nishimori K, et al. Effects of bifidobacterial supplementation to pregnant women and infants in the prevention of allergy development in infants and on fecal microbiota. Allergol Int 2014;63(4):575-85. PubMed
  11. US Food and Drug Administration (FDA). Dear Healthcare Provider Letter: Warning Regarding Use of Probiotics in Preterm Infants. September 2023. Available at: https://www.fda.gov/media/172606/download?attachment. Accessed November 1, 2023.
  12. Pillai A, Tan J, Paquette V, Panczuk J. Does probiotic bacteremia in premature infants impact clinically relevant outcomes? A case report and updated review of literature. Clin Nutr ESPEN. 2020;39:255-259. PubMed
  13. Sabaté JM, Iglicki F. Effect of Bifidobacterium longum 35624 on disease severity and quality of life in patients with irritable bowel syndrome. World J Gastroenterol 2022;28(7):732-744.
  14. Malaguarnera M, Greco F, Barone G, Gargante MP, Malaguarnera M, Toscano MA. Bifidobacterium longum with fructo-oligosaccharide (FOS) treatment in minimal hepatic encephalopathy: a randomized, double-blind, placebo-controlled study. Dig Dis Sci 2007;52(11) PubMed
  15. Zbinden A, Zbinden R, Berger C, Arlettaz R. Case series of Bifidobacterium longum bacteremia in three preterm infants on probiotic therapy. Neonatology 2015;107(1):56-9.

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Bifidobacterium Longum and Levothyroxine Together: Common Questions

Is it safe to take Bifidobacterium Longum with Levothyroxine?
We do not list a known interaction between Bifidobacterium Longum and Levothyroxine. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Should I take Bifidobacterium Longum and Levothyroxine at the same time of day?
At least one FDA label for a product containing Levothyroxine says to take it on an empty stomach, and supplements are usually taken with a meal — so taking them together at breakfast is the easy mistake. Where that applies, keep Levothyroxine on its own and move Bifidobacterium Longum to a meal later in the day. Food instructions belong to the product rather than the ingredient, so check the directions on your own box. This is about absorption, not an interaction.
Are Bifidobacterium Longum and Levothyroxine used for the same thing?
They overlap in purpose, which usually means the real question is whether you need both rather than whether they are safe together. This page lists the shared uses and how strong the evidence is for Bifidobacterium Longum in each. That is a conversation for your prescriber, especially if Levothyroxine is being adjusted to a target.
How was the Bifidobacterium Longum and Levothyroxine combination checked?
Interactions in our licensed database are recorded against drug classes. Levothyroxine is filed under 3 classifications, and Bifidobacterium Longum has documented interactions with 1 drug class — none of Levothyroxine's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does Bifidobacterium Longum interact with any other medications?
Yes. Bifidobacterium Longum has 182 documented drug interactions in our database — Levothyroxine is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Levothyroxine interact with any supplements?
Yes. Levothyroxine has documented interactions with 50 supplements in our database — Bifidobacterium Longum is not one of them. The Levothyroxine interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

Bifidobacterium Longum monograph Uses, safety profile, and every drug interaction in one place Levothyroxine drug information The full plain-English guide to this medication Levothyroxine supplement interactions Every supplement checked against Levothyroxine, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 21 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Levothyroxine and Bifidobacterium Longum?

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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.