Drug & supplement interaction

Fluoride + 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 Fluoride 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, and the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Fluoride 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 Fluoride 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.

Worth understanding: our licensed dataset holds no drug-interaction record for Fluoride at all — not against Levothyroxine, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

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.

Fluoride safety at a glance

Fluoride overall Use caution Safe at recommended dental doses, but excess can cause fluorosis and other harm.
Pregnancy Likely Safe When used orally and appropriately. Elemental fluoride is safe when used in doses below the tolerable upper intake level (UL) of 10 mg daily. Although fluoridat... Read the full pregnancy detail
Breastfeeding Likely Safe When used orally and appropriately. Elemental fluoride is safe when used in doses below the tolerable upper intake level (UL) of 10 mg daily. Although fluoridat... 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 Fluoride? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

No Interaction Found — But Data Suggests Fluoride and Levothyroxine May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do. 3 of them are worth acting on rather than waiting out — marked below.

  • A change in thyroid levels Worth acting on Additional detail

    Fluoride

    “Some in vitro and observational research has raised concerns regarding the impact of increased fluoride intake on thyroid function. The available observational research, which has taken place in multiple countries with highly variable water fluoride concentrations, has yielded conflicting findings. Some of these conflicting findings may relate to the use of urinary fluoride levels to estimate fluoride exposure.”

    Fluoride · Natural Medicines adverse-effect record, reported in hypothyroidism.

    5 sources cited
    1. 115603. Griebel-Thompson AK, Sands S, Chollet-Hinton L, et al. A Scoping Review of Iodine and Fluoride in Pregnancy in Relation to Maternal Thyroid Function and Offspring Neurodevelopment. Adv Nutr 2023;14(2):317-338. PubMed
    2. 114885. Mou Y, Qu T, Wang R, Zhang Y, He Z, Gu S. The association of high-fluoride and high-iodine combined exposure with dental fluorosis and goiter: a meta-analysis. Environ Geochem Health 2023;45(6):3143-3153. PubMed
    3. 114889. Malin AJ, Riddell J, McCague H, Till C. Fluoride exposure and thyroid function among adults living in Canada: Effect modification by iodine status. Environ Int 2018;121(Pt 1):667-674. PubMed
    4. 114884. Iamandii I, De Pasquale L, Giannone ME, et al. Does fluoride exposure affect thyroid function? A systematic review and dose-response meta-analysis. Environ Res 2024;242:117759. PubMed
    5. 114886. Hall M, Lanphear B, Chevrier J, Hornung R, Green R, Goodman C, et al. Fluoride exposure and hypothyroidism in a Canadian pregnancy cohort. Sci Total Environ 2023;869:161149. PubMed

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

  • Hives / An allergic reaction Worth acting on Additional detail

    Fluoride

    “Exposure to fluoride can cause allergic reactions including urticaria, exfoliative dermatitis, atopic dermatitis, stomatitis, and gastrointestinal allergic reactions. Respiratory allergic reactions occur rarely (15,94408). A case of dermatitis around the mouth was thought to be related to the high fluoride levels in a specific toothpaste (NeutraFluor 5000 Plus).”

    Fluoride · Natural Medicines adverse-effect record, reported in dermatitis.

    4 sources cited
    1. 15. McEvoy GK, ed. AHFS Drug Information. Bethesda, MD: American Society of Health-System Pharmacists, 1998.
    2. 94408. Peters P, Drummond C. Perioral dermatitis from high fluoride dentifrice: a case report and review of literature. Aust Dent J. 2013 Sep;58(3):371-2. PubMed
    3. 94404. Foti C, Romita P, Ficco D, Bonamonte D, Angelini G. Allergic contact cheilitis to amine fluoride in a toothpaste. Dermatitis. 2014 Jul-Aug;25(4):209. PubMed
    4. 94403. Enamandram M, Das S, Chaney KS. Cheilitis and urticaria associated with stannous fluoride in toothpaste. J Am Acad Dermatol. 2014 Sep;71(3):e75-6. PubMed

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

  • A skin rash Additional detail

    Fluoride

    Recorded for Fluoride in the same Natural Medicines adverse-effect record shown under Hives / An allergic reaction above.

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

  • Vomiting / Nausea Additional detail

    Fluoride

    “Orally, fluoride can cause gastrointestinal symptoms. Enteric-coated and sustained-release dosage forms of sodium phosphate and sodium monofluorophosphate may cause fewer adverse effects than plain sodium fluoride. Adverse effects appear to be dose related. Sodium fluoride at high daily doses of 40-65 mg can cause nausea, vomiting, and GI bleeding (15,9127).”

    Fluoride · Natural Medicines adverse-effect record, reported in myasthenia gravis.

    4 sources cited
    1. 94405. Grey A, Garg S, Dray M, Purvis L, Horne A, Callon K, Gamble G, Bolland M, Reid IR, Cundy T. Low-dose fluoride in postmenopausal women: a randomized controlled trial. J Clin Endocrinol Metab. 2013 Jun;98(6):2301-7. PubMed
    2. 9127. Brown JP, Josse RG, et al. 2002 clinical practice guidelines for the diagnosis and management of osteoporosis in Canada. CMAJ 2002;167:S1-S34..
    3. 9129. Haguenauer D, Welch V, Shea B, et al. Fluoride for treating postmenopausal osteoporosis.(Cochrane Review). Cochrane Database Syst Rev 2002;(4):CD002825.. PubMed
    4. 15. McEvoy GK, ed. AHFS Drug Information. Bethesda, MD: American Society of Health-System Pharmacists, 1998.

    Levothyroxine

    Listed in the ADVERSE REACTIONS section of the FDA label for Levothyroxine. Read the label on DailyMed ›

Reported for Fluoride but not commonly for Levothyroxine: a severe skin reaction, joint or muscle stiffness, raised blood pressure and bleeding in the gut.

Effects for Levothyroxine come from the ADVERSE REACTIONS section of its FDA label; effects for Fluoride come from the Natural Medicines adverse-effect record, quoted above. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

Fluoride in Pregnancy & Breastfeeding

Pregnancy And Lactation Likely Safe

When used orally and appropriately. Elemental fluoride is safe when used in doses below the tolerable upper intake level (UL) of 10 mg daily. Although fluoridated water has been consumed during pregnancy with apparent safety for many years, some population research suggests that more information is needed to determine a safe level of fluoride exposure for those living in regions with fluoridated water. Some emerging population research suggests that increased urinary fluoride levels during pregnancy might be associated with negative cognitive effects in the infant. However, more information is needed to determine if these results are clinically significant at the population level, as well as whether these effects are due to fluoride or to confounding factors such as socioeconomic status, use of formula instead of breast-feeding, lifestyle factors present during pregnancy, other regional environmental exposures, or the choice of IQ tests used in studies. ...when used topically and appropriately. Fluoride is safe in quantities typically found in toothpastes, mouth rinses, and professionally applied fluoride dental treatments.

Pregnancy And Lactation Possibly Unsafe

When used orally at doses above the tolerable upper intake level (UL) of 10 mg daily of elemental fluoride for prolonged periods. Long-term exposure to high doses can cause skeletal fluorosis, but pregnancy or lactation doesn't seem to affect susceptibility to skeletal fluorosis.

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 — Fluoride Should Not Break It

At least one FDA label for a product containing Levothyroxine says to take it on an empty stomach. Most supplements — Fluoride 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 Fluoride 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.

From our Q&A

Questions About Fluoride 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 Fluoride 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 Fluoride 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 Fluoride as Part of a Dietary Supplement Product? Check It for Interactions

We hold 61 real supplement products containing Fluoride, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Fluoride. Even though Fluoride 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 Fluoride 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 Fluoride
Top half

#546 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 Fluoride reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Fluoride 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 Fluoride

What is Fluoride?

  • Preventing tooth decay (cavities)
  • Strengthening tooth enamel
  • Dental care for children in low-fluoride areas
  • Bone health support

Fluoride is a mineral best known for preventing cavities and strengthening tooth enamel, and it is widely used in toothpaste, mouth rinses, and community water. Supplements (drops or tablets) are sometimes prescribed for children in areas without fluoridated water, but they should be used only under professional guidance because too much fluoride can harm teeth and bones. Always check with your dentist, doctor, or pharmacist before giving fluoride supplements.

Mineral (fluoride ion) · Tablets, lozenges, drops, mouth rinses, toothpaste, varnish, fluoridated water, and combination supplements

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

Fluoride: dosing

There is no single supplement dose that fits everyone. The amount of fluoride a person needs depends on their age and how much fluoride is already in their drinking water. Because of this, fluoride supplement dosing for children is decided by a dentist or doctor.For everyday use, follow the directions on your toothpaste or mouth rinse label, and use only a small (pea-sized or smaller) amount of toothpaste for young children.

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

Read the full Fluoride 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 & Fluoride

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

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

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Fluoride list.

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

Fluoride References

The 39 references that drive our Fluoride 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. McEvoy GK, ed. AHFS Drug Information. Bethesda, MD: American Society of Health-System Pharmacists, 1998.
  2. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press, 1999. Available at: http://books.nap.edu/books/0309063507/html/index.html.
  3. Position of the American Dietetic Association: the impact of fluoride on health. J Am Diet Assoc 2001;101:126-32.. PubMed
  4. Brown JP, Josse RG, et al. 2002 clinical practice guidelines for the diagnosis and management of osteoporosis in Canada. CMAJ 2002;167:S1-S34..
  5. Haguenauer D, Welch V, Shea B, et al. Fluoride for treating postmenopausal osteoporosis.(Cochrane Review). Cochrane Database Syst Rev 2002;(4):CD002825.. PubMed
  6. Choi AL, Sun G, Zhang Y, Grandjean P. Developmental fluoride neurotoxicity: a systematic review and meta-analysis. Environ Health Perspect. 2012 Oct;120(10):1362-8. PubMed
  7. Enamandram M, Das S, Chaney KS. Cheilitis and urticaria associated with stannous fluoride in toothpaste. J Am Acad Dermatol. 2014 Sep;71(3):e75-6. PubMed
  8. Foti C, Romita P, Ficco D, Bonamonte D, Angelini G. Allergic contact cheilitis to amine fluoride in a toothpaste. Dermatitis. 2014 Jul-Aug;25(4):209. PubMed
  9. Grey A, Garg S, Dray M, Purvis L, Horne A, Callon K, Gamble G, Bolland M, Reid IR, Cundy T. Low-dose fluoride in postmenopausal women: a randomized controlled trial. J Clin Endocrinol Metab. 2013 Jun;98(6):2301-7. PubMed
  10. Peters P, Drummond C. Perioral dermatitis from high fluoride dentifrice: a case report and review of literature. Aust Dent J. 2013 Sep;58(3):371-2. PubMed
  11. Sälzer S, Slot DE, Dörfer CE, Van der Weijden GA. Comparison of triclosan and stannous fluoride dentifrices on parameters of gingival inflammation and plaque scores: a systematic review and meta-analysis. Int J Dent Hyg. 2015 Feb;13(1):1-17.
  12. Till C, Green R, Flora D, et al. Fluoride exposure from infant formula and child IQ in a Canadian birth cohort. Environ Int. 2020;134:105315. PubMed
  13. Seddek AL, Ghallab A. Fluoride: No evidence of developmental neurotoxicity due to current exposure levels in Europe. Arch Toxicol. 2020;94(7):2543-2544. PubMed
  14. Green R, Lanphear B, Hornung R, et al. Association between maternal fluoride exposure during pregnancy and IQ scores in offspring in Canada. JAMA Pediatr. 2019;173(10):940-8. PubMed
  15. Guth S, Hüser S, Roth A, et al. Toxicity of fluoride: critical evaluation of evidence for human developmental neurotoxicity in epidemiological studies, animal experiments and in vitro analyses. Arch Toxicol. 2020;94(5):1375-1415. PubMed

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 Fluoride and Levothyroxine Together: Common Questions

Is it safe to take Fluoride with Levothyroxine?
We do not list a known interaction between Fluoride 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.
Do Fluoride and Levothyroxine have any of the same side effects?
Yes — our sources link each of them separately to 6 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
Should I take Fluoride 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 Fluoride 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.
Does Levothyroxine interact with any supplements?
Yes. Levothyroxine has documented interactions with 50 supplements in our database — Fluoride 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

Fluoride 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 39 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Levothyroxine and Fluoride?

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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.