Best Thyroid Supplements: 11 Picks Ranked by Evidence

Quick Summary

Is there a thyroid supplement that actually works? For most people, the useful thyroid supplements are the ones that fix a measured shortfall, not the ones labeled “thyroid support.” No supplement replaces thyroid hormone medication: levothyroxine remains the standard treatment for hypothyroidism ^[1]. Selenium has the most trial evidence, lowering thyroid peroxidase (TPO) antibodies in people with Hashimoto thyroiditis ^[2][3]. Myo-inositol combined with selenium has smaller trials in subclinical hypothyroidism ^[4][5]. Iron, vitamin B12 and vitamin D help when a blood test shows they are low, and those shortfalls are more common alongside thyroid disease ^[6][7]. Iodine is only for low intake. Skip “thyroid support” blends and glandulars: many contain real thyroid hormone ^[8].

Introduction

“Which supplement will help my thyroid?”

Search for thyroid supplements and most of what you find is a multi-ingredient “thyroid support” formula: iodine or kelp, an herb such as ashwagandha or guggul, tyrosine, sometimes dried animal thyroid tissue. These products are sold as a way to support the gland without medication. The evidence points the other way. When researchers bought 10 thyroid supplements and measured their contents, 9 contained the thyroid hormone T3 and 5 contained T4 ^[8]. Taken at the label dose, 5 delivered more than 10 mcg of T3 a day, and some exceeded common treatment doses ^[8].

The supplements with real evidence are single nutrients. Your thyroid needs iodine to make its hormones, selenium to protect itself while making them and to convert T4 into active T3, and iron to run thyroid peroxidase, the enzyme that builds the hormone ^[6]. When one of these runs short, thyroid function can suffer. When your levels are adequate, more rarely helps.

That is why this guide is organized by need rather than by product. Each section names the situation where a nutrient has evidence, what that evidence found, and which test tells you whether it applies to you.

What makes a good thyroid supplement:

• One nutrient with a dose stated per serving, so you know exactly what you are taking
• The form used in the trials (selenomethionine, myo-inositol, iron bisglycinate or another chelated iron, methylcobalamin, vitamin D3)
• Third-party testing or a GMP-certified facility
• No hidden thyroid hormone, glandular tissue or high-dose iodine

What to avoid:

• “Thyroid support” blends that list thyroid glandular, bovine thyroid or “thyroid tissue”
• Iodine or kelp at doses above the adult upper limit of 1,100 mcg a day ^[9]
• Biotin in the days before a thyroid blood test ^[10]
• Iron or calcium taken at the same time as levothyroxine ^[11][12]

Which Thyroid Supplement Fits Your Situation?

Top picks

Reviews

Each card shows the current price from the Mito catalog.

Best for Raised TPO Antibodies: Selenium (Selenomethionine)

Selenium is the most studied thyroid supplement. Selenium-based enzymes protect the thyroid from the hydrogen peroxide it makes while building hormone ^[6]. A 2024 meta-analysis of 35 randomized trials in people with Hashimoto thyroiditis found that selenium lowered TPO antibodies, whether or not people were taking thyroid hormone, and lowered TSH slightly in people not on medication ^[3]. Free T4 and free T3 did not change, and adverse effects were similar to placebo ^[3]. An earlier meta-analysis reached the same antibody result but rated the evidence as low quality, found slightly more reported side effects with selenium, and noted that the link to how people feel remains unproven ^[2]. Several of the trials used 200 mcg a day of selenomethionine ^[13]. If you do not have raised TPO antibodies, there is little trial evidence for extra selenium.

The adult upper limit for selenium is 400 mcg a day from all sources, and Brazil nuts and multivitamins count toward it ^[14]. Both picks below use L-selenomethionine at 200 mcg, the form and amount in those trials.

Best for Third-party tested selenomethionine with a two-ingredient capsule

1. Thorne Selenium

• Form: L-selenomethionine
• Selenium per Capsule: 200 mcg
• Label Serving: 1 capsule
• Third-Party Testing: Third-party tested and certified, per the label
• Bottle: 60 capsules (60 servings)
• Best For: Third-party tested selenomethionine with a two-ingredient capsule

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Selenium is an important trace mineral and an essential nutrient that your body needs.

Pros

• Same form and amount as several Hashimoto trials
• Only two other ingredients
• Free of gluten, dairy and soy

Cons

• 60-capsule bottle only
• Adds up quickly with a multivitamin that also contains selenium

Best for Yeast-free selenomethionine in a larger bottle

2. NOW Foods Selenium 200 mcg

• Form: L-selenomethionine, yeast-free
• Selenium per Capsule: 200 mcg
• Label Serving: 1 capsule with a meal
• Third-Party Testing: Made in a GMP facility
• Bottle: 180 capsules (180 servings)
• Best For: Yeast-free selenomethionine in a larger bottle

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Selenium is an essential trace mineral that is found naturally in Brazil nuts, organ meats, seafood, and wheat germ.

Pros

• 180 capsules per bottle
• Yeast-free, which suits people avoiding selenium yeast
• Vegetarian capsule

Cons

• Made in a facility that processes common allergens
• Label advises people in high-selenium soil areas, such as the Dakotas, to check with a physician first

For more on how TPO antibodies relate to Hashimoto and Graves disease, see Hashimoto’s vs Graves’ disease.

Best for Subclinical Hypothyroidism With Antibodies: Myo-Inositol

Myo-inositol is part of the signaling chain TSH uses inside thyroid cells ^[4]. Two randomized trials from the same research group tested it with selenium in people with autoimmune thyroiditis and subclinical hypothyroidism, a mildly raised TSH with normal T4. In the first, 48 women took 83 mcg of selenomethionine a day, with or without 600 mg of myo-inositol, for six months; TSH and antibodies fell further with the combination ^[4]. In the second, 168 people with Hashimoto and a TSH between 3 and 6 took the combination or selenium alone; TSH and both thyroid antibodies fell more with the combination after six months ^[5]. These are small trials from one group, and independent replication is limited.

No single in-stock product matches the trial combination of myo-inositol and selenomethionine in one capsule, so the picks below are plain myo-inositol.

Best for Myo-inositol capsule free of the common allergens

1. Jarrow Formulas Inositol 750 mg

• Form: Myo-inositol
• Inositol per Capsule: 750 mg
• Label Serving: 1 capsule
• Bottle: 100 capsules (100 servings)
• Best For: Myo-inositol capsule free of the common allergens

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Jarrow Formulas® Inositol is readily absorbed and used to produce the active inositides as necessary.

Pros

• Labeled as myo-inositol, the form in the trials
• Free of wheat, gluten, soy, dairy and nuts
• Vegetarian capsule

Cons

• Contains no selenium, unlike the trial capsule
• Higher per-capsule amount than the trials used

Best for Lower per-capsule amount of myo-inositol

2. NOW Foods Inositol 500 mg

• Form: Myo-inositol
• Inositol per Capsule: 500 mg
• Label Serving: 1 capsule
• Bottle: 100 capsules (100 servings)
• Best For: Lower per-capsule amount of myo-inositol

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Inositol is a non-essential member of the B-Complex family with dietary sources from both animal and plant foods.

Pros

• Labeled as myo-inositol
• Short ingredient list
• Vegetarian capsule

Cons

• Contains no selenium, unlike the trial capsule
• Label is for adults only

Best for Low Ferritin: Iron Bisglycinate

Thyroid peroxidase, the enzyme that makes thyroid hormone, only works once it binds iron ^[6]. People with Hashimoto thyroiditis are often low in iron, partly because autoimmune gastritis, which reduces iron absorption, is common alongside it ^[6]. A review of women with hypothyroidism recommends checking iron and ferritin as part of the workup ^[15]. The same review by Hu and Rayman reports that iron given to anemic women with impaired thyroid function improved their thyroid hormone levels ^[6]. Take iron only after a low ferritin or iron result.

If you take levothyroxine, iron matters for timing as well. In 14 people with hypothyroidism who took ferrous sulfate together with their usual levothyroxine for 12 weeks, TSH rose and some had more hypothyroid symptoms ^[11]. Your prescribing clinician can tell you how far apart to take them.

Best for Low ferritin confirmed on a blood test, sensitive stomach

1. Thorne Iron Bisglycinate

• Form: Ferrous bisglycinate chelate (Ferrochel)
• Iron per Capsule: 25 mg
• Label Serving: 1 capsule
• Third-Party Testing: NSF version of Thorne Iron Bisglycinate
• Bottle: 60 capsules (60 servings)
• Best For: Low ferritin confirmed on a blood test, sensitive stomach

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Iron is essential to the formation and function of healthy red blood cells.

Pros

• Chelated form marketed as gentler on the stomach than ferrous sulfate
• Short ingredient list
• Moderate per-capsule dose

Cons

• Contains no vitamin C, which some people pair with iron to aid absorption

Best for Vegan iron with a longer-lasting bottle

2. Klaire Labs Iron Chelate

• Form: Ferrous bisglycinate chelate (Albion Ferrochel)
• Iron per Capsule: 30 mg
• Label Serving: 1 capsule with food
• Bottle: 100 capsules (100 servings)
• Best For: Vegan iron with a longer-lasting bottle

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This compound has been shown to be a well-tolerated, bioavailable form of iron.

Pros

• Vegan and made without common allergens
• 100 capsules per bottle
• Same chelated iron form as the Thorne pick

Cons

• Label says it is not intended for children

For more on iron forms, see the best iron supplement for anemia.

Best for Low B12: Vitamin B12 (Methylcobalamin)

Vitamin B12 runs lower in people with hypothyroidism. A 2023 meta-analysis found lower average B12 in people with hypothyroidism than in healthy controls, and about 27% of people with hypothyroidism across the included studies were B12 deficient ^[7]. Low B12 causes tiredness and anemia, which overlap with hypothyroid symptoms, so a B12 test helps separate the two. Deficiency is also more likely in vegans, older adults and people on long-term metformin or acid reducers ^[16].

Best for Vegans, adults over 50, long-term metformin or acid-reducer use

1. Jarrow Formulas Methyl B-12 1000 mcg

• Form: Methylcobalamin, lemon chewable
• B12 per Tablet: 1,000 mcg
• Label Serving: 1 tablet, dissolved in the mouth or chewed
• Bottle: 100 chewables (100 servings)
• Best For: Vegans, adults over 50, long-term metformin or acid-reducer use

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Methylcobalamin (Methyl B-12) is better absorbed and retained than other forms of B12 (e.g., cyanocobalamin).

Pros

• Dose in the range a clinical review reports for oral repletion
• Free of wheat, gluten, soy and dairy
• More than three months per bottle

Cons

• Sweetened with xylitol
• Lemon flavor only

Best for Dissolvable lozenge in a smaller bottle

2. Life Extension Vitamin B12 Methylcobalamin 1 mg Lozenges

• Form: Methylcobalamin, vanilla lozenge
• B12 per Lozenge: 1 mg (1,000 mcg)
• Label Serving: 1 lozenge
• Bottle: 60 lozenges (60 servings)
• Best For: Dissolvable lozenge in a smaller bottle

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Vitamin B12, also called cobalamin, is a water-soluble vitamin.

Pros

• Dissolves in the mouth, no swallowing
• Vegetarian and non-GMO

Cons

• Contains sorbitol and xylitol
• Smaller bottle than the Jarrow pick

Best for Low Vitamin D: Vitamin D3

People with Hashimoto thyroiditis tend to have lower vitamin D than people without it ^[17]. Two meta-analyses of supplementation trials in Hashimoto found lower TPO antibodies with vitamin D: one pooled 8 studies with 652 people and saw the effect with vitamin D3 taken for more than three months ^[18], and another pooled 12 studies with 862 people ^[19]. The trials were small and varied widely, and one review argues that low vitamin D may be a result of autoimmune disease rather than a cause ^[6]. A vitamin D test tells you whether you are low to begin with.

Best for Hypoallergenic, low per-capsule dose that is easy to adjust

1. Pure Encapsulations Vitamin D3 1,000 IU

• Form: Cholecalciferol (vitamin D3)
• Vitamin D per Capsule: 25 mcg (1,000 IU)
• Label Serving: 1 capsule with food
• Bottle: 60, 120 or 250 capsules (1 capsule per serving)
• Best For: Hypoallergenic, low per-capsule dose that is easy to adjust

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Vitamin D3 naturally supports calcium absorption and retention within bones to promote optimal bone health.

Pros

• Hypoallergenic and vegetarian
• Low per-capsule dose that fits retesting and adjustment
• Three bottle sizes

Cons

• Label advises monitoring blood levels for people taking more than 2,000 IU a day

Best for Vitamin D3 paired with vitamin K2

2. Carlson Labs Adult D3 & K2

• Form: Vitamin D3 (cholecalciferol) with vitamin K2 as MK-7
• Amount per Serving: 50 mcg (2,000 IU) D3 and 90 mcg K2 per 2 capsules
• Label Serving: 2 capsules at mealtime
• Bottle: 120 capsules (60 servings)
• Best For: Vitamin D3 paired with vitamin K2

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Vitamin D3 and K2 as MK-7 work synergistically to support cardiovascular system and bone health.

Pros

• D3 and K2 in one product
• Vegetable capsule

Cons

• Two-capsule serving
• Label warns that vitamin K can counteract warfarin

Best for Low Iodine Intake: Iodine (Potassium Iodide)

Iodine is the raw material of thyroid hormone, and adults need 150 mcg a day ^[9]. Most people in the US get enough from iodized salt, dairy, eggs and seafood ^[9]. People who avoid all of those, such as vegans who skip iodized salt, are the group most likely to fall short. The American Thyroid Association recommends a supplement with 150 mcg of iodine a day before and during pregnancy and while breastfeeding ^[9].

More is not better. Chronic high iodine intake can trigger autoimmune thyroiditis ^[6], and the adult upper limit is 1,100 mcg a day from all sources ^[9]. People with autoimmune thyroid disease can have side effects at intakes that are safe for most people ^[9], and the label of the pick below warns that iodine may be contraindicated with thyroid medications.

Best for Single-ingredient iodine well under the upper limit

1. Pure Encapsulations Iodine (Potassium Iodide)

• Form: Potassium iodide
• Iodine per Capsule: 225 mcg
• Label Serving: 1 capsule with a meal
• Bottle: 120 capsules (120 servings)
• Best For: Single-ingredient iodine well under the upper limit

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Iodine is designed to provide natural support for the thyroid gland and helps to maintain healthy cellular metabolism.

Pros

• One ingredient, no kelp or herbs
• Hypoallergenic and vegan
• Per-capsule amount far below the 1,100 mcg upper limit

Cons

• Label says it may be contraindicated with thyroid medications
• Not suited to people who already get enough iodine

What to Look For in a Thyroid Supplement

1. A Test Result That Points to It

Each nutrient above has its clearest evidence in a specific group: selenium and myo-inositol in people with raised thyroid antibodies, and iron, B12 and vitamin D in people who are low ^[3][5][6][7]. A blood test tells you which group you are in.

2. No Thyroid Hormone, Glandulars or Hidden Iodine

Products sold for “thyroid support” have been found to contain T3 and T4 at clinically relevant amounts ^[8]. Hidden thyroid hormone can push your thyroid levels too high, and the researchers warned it can go as far as thyrotoxicosis ^[8]. Avoid labels that list thyroid glandular, bovine thyroid or “thyroid tissue,” and check the iodine or kelp amount against the 1,100 mcg upper limit ^[9]. Multi-herb blends with iodine, tyrosine, ashwagandha or guggul make it hard to know what you are taking at what dose.

3. The Form and Amount on the Label

• Selenium: selenomethionine at 200 mcg is the form and amount used in several trials ^[13].
• Myo-inositol: the trials used 600 mg with 83 mcg of selenomethionine ^[4].
• Iron: chelated forms such as bisglycinate are marketed as gentler on the stomach.
• B12: methylcobalamin and cyanocobalamin both raise B12 levels.
• Vitamin D: D3 (cholecalciferol) is the form in most trials.
• Iodine: potassium iodide states an exact amount; kelp content varies.

4. No Biotin Before a Thyroid Test

Biotin, common in hair, skin and nail products, interferes with many lab tests. In 6 healthy adults taking 10 mg of biotin a day for a week, 9 of 23 biotin-based lab tests gave falsely high or falsely low results, and the tests studied included TSH, free T4 and free T3 ^[10]. Pause biotin before a thyroid blood test and tell whoever orders it that you take it.

5. Timing Around Thyroid Medication

Iron and calcium bind levothyroxine in the gut. Taking 1,200 mg of calcium as calcium carbonate with levothyroxine for three months lowered free T4 and raised TSH in 20 people with hypothyroidism ^[12]. Iron showed a similar effect ^[11].

6. Quality Signals

Look for third-party certification such as NSF or USP, or at minimum manufacturing in a GMP-certified facility. For what each seal does and does not verify, see how to choose a supplement brand.

Cost Comparison

Each product card above shows its current price from the Mito catalog. To compare cost per serving, divide that price by the servings per bottle below.

Test This with Mito

The right thyroid supplement depends on your results, so test first. Retesting after a few months tells you whether your levels moved.

• Thyroid-stimulating hormone (TSH): the standard first test of thyroid function. For how to read it, see TSH results explained.
• Free thyroxine (free T4): the main hormone the thyroid releases.
• Free triiodothyronine (free T3): the active form, made mostly from T4. See free T3 vs free T4.
• Thyroid peroxidase antibody (TPO): the antibody the selenium and myo-inositol trials measured. To check thyroglobulin antibodies too, choose the TPO and thyroglobulin antibodies panel.
• Ferritin: your iron stores, before you take iron.
• Vitamin B12 and folate panel: the B12 shortfall more common in hypothyroidism.
• Vitamin D, 25-hydroxy: the standard measure of your vitamin D status.
• Selenium: your current selenium level, given the 400 mcg upper limit.
• Mito Core Panel: includes TSH, total T4, T3 uptake, free T4 and free T3, plus ferritin, B12, folate and vitamin D, with clinician-reviewed results. It does not include TPO antibodies.

To compare thyroid tests side by side, read the best thyroid test.

Key Takeaways

• No supplement replaces thyroid medication: levothyroxine remains the standard treatment for hypothyroidism.
• Selenium has the most evidence, for lowering TPO antibodies in Hashimoto thyroiditis.
• Myo-inositol with selenium has two small trials in subclinical hypothyroidism.
• Iron, B12 and vitamin D help when you are low, and those shortfalls are common with thyroid disease.
• Iodine is only for low intake; too much can worsen autoimmune thyroid disease.
• Skip “thyroid support” blends and glandulars, which may contain real thyroid hormone.
• Pause biotin before a thyroid test, and keep iron and calcium apart from levothyroxine.

Related Content

• How to Raise Thyroid Levels Naturally
• The Best Thyroid Test
• TSH Results Explained
• Hashimoto’s vs Graves’ Disease: Autoimmune Thyroid Testing
• Free T3 vs Free T4: Understanding Your Thyroid Blood Test
• Best Supplements for Energy
• Best Iron Supplement for Anemia

Medical Disclaimer

This article is for educational purposes only and is not medical advice. It does not diagnose or treat any condition, and the supplements it covers are not a treatment for thyroid disease.

References

1. Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid. 2014;24(12):1670-1751. PMC4267409
2. Wichman J, Winther KH, Bonnema SJ, Hegedüs L. Selenium Supplementation Significantly Reduces Thyroid Autoantibody Levels in Patients with Chronic Autoimmune Thyroiditis: A Systematic Review and Meta-Analysis. Thyroid. 2016;26(12):1681-1692. PMID: 27702392
3. Huwiler VV, Maissen-Abgottspon S, Stanga Z, et al. Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Thyroid. 2024;34(3):295-313. PMC10951571
4. Nordio M, Pajalich R. Combined treatment with Myo-inositol and selenium ensures euthyroidism in subclinical hypothyroidism patients with autoimmune thyroiditis. J Thyroid Res. 2013;2013:424163. PMC3809375
5. Nordio M, Basciani S. Myo-inositol plus selenium supplementation restores euthyroid state in Hashimoto’s patients with subclinical hypothyroidism. Eur Rev Med Pharmacol Sci. 2017;21(2 Suppl):51-59. PMID: 28724185
6. Hu S, Rayman MP. Multiple Nutritional Factors and the Risk of Hashimoto’s Thyroiditis. Thyroid. 2017;27(5):597-610. PMID: 28290237
7. Benites-Zapata VA, Ignacio-Cconchoy FL, Ulloque-Badaracco JR, et al. Vitamin B12 levels in thyroid disorders: A systematic review and meta-analysis. Front Endocrinol (Lausanne). 2023;14:1070592. PMC9994182
8. Kang GY, Parks JR, Fileta B, et al. Thyroxine and triiodothyronine content in commercially available thyroid health supplements. Thyroid. 2013;23(10):1233-1237. PMID: 23758055
9. NIH Office of Dietary Supplements. Iodine: Fact Sheet for Health Professionals. ods.od.nih.gov
10. Li D, Radulescu A, Shrestha RT, et al. Association of Biotin Ingestion With Performance of Hormone and Nonhormone Assays in Healthy Adults. JAMA. 2017;318(12):1150-1160. PMC5818818
11. Campbell NR, Hasinoff BB, Stalts H, et al. Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism. Ann Intern Med. 1992;117(12):1010-1013. PMID: 1443969
12. Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. JAMA. 2000;283(21):2822-2825. PMID: 10838651
13. van Zuuren EJ, Albusta AY, Fedorowicz Z, et al. Selenium supplementation for Hashimoto’s thyroiditis. Cochrane Database Syst Rev. 2013;(6):CD010223. PMC9862303
14. NIH Office of Dietary Supplements. Selenium: Fact Sheet for Health Professionals. ods.od.nih.gov
15. Gierach M, Rudewicz M, Junik R. Iron and ferritin deficiency in women with hypothyroidism and chronic lymphocytic thyroiditis: systematic review. Endokrynol Pol. 2024;75(3):253-261. PMID: 38923898
16. Langan RC, Goodbred AJ. Vitamin B12 Deficiency: Recognition and Management. Am Fam Physician. 2017;96(6):384-389. PMID: 28925645
17. Wang J, Lv S, Chen G, et al. Meta-analysis of the association between vitamin D and autoimmune thyroid disease. Nutrients. 2015;7(4):2485-2498. PMC4425156
18. Zhang J, Chen Y, Li H, Li H. Effects of vitamin D on thyroid autoimmunity markers in Hashimoto’s thyroiditis: systematic review and meta-analysis. J Int Med Res. 2021;49(12):3000605211060675. PMC8711703
19. Tang J, Shan S, Li F, Yun P. Effects of vitamin D supplementation on autoantibodies and thyroid function in patients with Hashimoto’s thyroiditis: A systematic review and meta-analysis. Medicine (Baltimore). 2023;102(52):e36759. PMC10754614

Frequently asked questions

Is there a thyroid supplement that actually works?

No supplement replaces thyroid hormone medication, and the American Thyroid Association guideline keeps levothyroxine as the standard treatment for hypothyroidism. Selenium has the most trial evidence: in people with Hashimoto thyroiditis it lowered thyroid peroxidase (TPO) antibodies, though whether that changes how people feel is not settled. Iron, vitamin B12 and vitamin D help when a blood test shows they are low.

What are the best supplements for hypothyroidism?

The supplements with evidence in people with an underactive thyroid are the ones that correct a measured shortfall: iron when ferritin is low, B12 when B12 is low and vitamin D when vitamin D is low. Selenium has been studied mostly in Hashimoto thyroiditis, the most common cause of hypothyroidism in countries with enough iodine, such as the US. None of them raises thyroid hormone the way medication does.

Should I take iodine for my thyroid?

Only if your iodine intake is low. Most people in the US get enough iodine from iodized salt, dairy, eggs and seafood. The adult upper limit is 1,100 mcg a day, and too much iodine can cause or worsen thyroid problems, especially in people with autoimmune thyroid disease. People who avoid iodized salt, dairy and seafood are the group most likely to fall short.

Are thyroid support supplements safe?

Many are not what their labels suggest. When researchers tested 10 thyroid support supplements, 9 contained the thyroid hormone T3 and 5 contained T4, some at amounts above common treatment doses. Products listing thyroid glandular or bovine thyroid tissue, or high-dose iodine or kelp, carry the most risk of changing your thyroid levels.

Can biotin affect a thyroid blood test?

Yes. Biotin, common in hair, skin and nail supplements, can make some lab tests read falsely high or falsely low. In a study of healthy adults taking 10 mg of biotin a day for a week, 9 of 23 biotin-based lab tests gave false results, and the tests studied included TSH, free T4 and free T3. Pause biotin before a thyroid blood test and tell whoever orders the test that you take it.

Do I take thyroid supplements at the same time as levothyroxine?

Iron and calcium supplements reduce how much levothyroxine your body absorbs when they are taken together. In one study, iron taken with levothyroxine raised TSH. In another, calcium carbonate taken with it lowered free T4 and raised TSH. Keeping them apart from your thyroid medication avoids that interaction.