What vitamins should you not take with Hashimoto's?

November 15, 2025 •

4 min read

According to the American Thyroid Association, high doses of the supplement biotin can interfere with laboratory tests for thyroid function, leading to false results. This highlights why understanding what vitamins you should not take with Hashimoto's is a critical part of managing this complex autoimmune condition and ensuring your treatment is effective.

Quick Summary

Hashimoto's patients should be cautious with certain supplements that can interfere with medication or thyroid function. Key vitamins and minerals to monitor include iodine, calcium, iron, and high-dose biotin. These can cause adverse effects, alter medication absorption, or compromise lab test accuracy.

Key Points

Avoid High-Dose Iodine: Excess iodine from supplements, including kelp, can exacerbate the autoimmune attack on the thyroid.
Separate Calcium and Iron Intake: Supplements containing calcium or iron should be taken at least four hours apart from your thyroid medication to prevent absorption interference.
Pause High-Dose Biotin Before Tests: To avoid inaccurate thyroid lab test results, inform your doctor and stop taking high-dose biotin supplements two to three days beforehand.
Use Caution with Herbs: Certain herbal supplements like ashwagandha, bugleweed, and lemon balm can have adverse or unpredictable effects on thyroid function in Hashimoto's patients.
Steer Clear of Glandular Supplements: Avoid over-the-counter thyroid glandular products, as they can contain unregulated hormones that interfere with prescribed medication.
Monitor Selenium Intake: While beneficial in moderation, excessive selenium (over 400 mcg/day) can lead to toxicity, so supplementation should be guided by a doctor.
Read Multivitamin Labels: Be aware that many multivitamins contain iodine, iron, and calcium, which are often best managed separately for Hashimoto's patients.

Hashimoto's thyroiditis is an autoimmune disorder where the immune system attacks the thyroid gland, often leading to hypothyroidism. While managing this condition, many people consider supplements to improve their health. However, some common vitamins, minerals, and herbal supplements can interfere with thyroid medication or worsen the underlying autoimmune process. This guide outlines what to avoid to ensure you are supporting, not sabotaging, your thyroid health.

The Problem with Excessive Iodine

Iodine is a mineral essential for producing thyroid hormones, but for people with Hashimoto's, excess intake can be problematic. High levels of iodine can paradoxically suppress thyroid function and may trigger or exacerbate the autoimmune attack on the thyroid gland. For this reason, many experts advise against routine iodine supplementation for most Hashimoto's patients unless a specific deficiency is diagnosed and managed by a healthcare provider.

Iodine-Rich Supplements to Avoid

Kelp and other seaweeds: Often found in supplements and marketed as 'thyroid boosters', these can contain very high concentrations of iodine that can worsen the condition.
Iodine drops or tablets: Unless prescribed for a proven deficiency, concentrated iodine supplements should be avoided entirely.

Minerals That Interfere with Medication Absorption

Thyroid hormone replacement medication, such as levothyroxine, needs to be properly absorbed to be effective. Certain minerals can bind to the medication in the digestive tract, significantly reducing its absorption and rendering the treatment less effective. Proper timing is key to managing these interactions.

Calcium and Iron

Both calcium and iron supplements are known to interfere with levothyroxine absorption. For this reason, they should not be taken at the same time as your thyroid medication. This also applies to multivitamins that contain these minerals. It is generally recommended to separate the intake of these supplements and your thyroid medication by at least four hours.

The Impact of Biotin on Lab Tests

High doses of biotin (vitamin B7), often taken for hair, skin, and nail health, can cause significant interference with thyroid function tests. This interference can lead to falsely high or low thyroid hormone readings (T4 and T3) and artificially low Thyroid Stimulating Hormone (TSH). Such inaccurate results can lead to misdiagnosis or inappropriate changes to your medication dosage.

How to Prevent Biotin Interference

Inform your doctor: Always tell your healthcare provider about any supplements you are taking, especially biotin, before a thyroid lab test.
Pause supplementation: The American Thyroid Association recommends stopping biotin intake at least two days before having thyroid function tests performed to avoid misleading results.

Other Supplements Requiring Caution

Beyond the most common vitamins and minerals, several other supplements should be approached with extreme caution due to their potential impact on Hashimoto's.

Herbal and Glandular Supplements

Ashwagandha: While this adaptogenic herb is sometimes touted for thyroid support, some studies suggest it may stimulate the immune system, potentially exacerbating the autoimmune response in Hashimoto's.
Bugleweed and Lemon Balm: These herbs are known to slow down thyroid function and are counterproductive for patients with hypothyroidism.
Over-the-Counter Thyroid Glandulars: These supplements contain desiccated animal thyroid glands and are not recommended. They can contain unregulated amounts of thyroid hormones that interfere with prescribed medication and lead to dangerous imbalances.

The Importance of Dosing with Selenium

Selenium is vital for thyroid hormone metabolism and can even help reduce thyroid antibodies in some autoimmune conditions when dosed appropriately. However, excessive intake (above 400 mcg/day) can be toxic, leading to side effects like hair loss and gastrointestinal upset. Selenium supplementation should only be done under medical guidance.

Navigating Multivitamins

Most commercial multivitamins contain ingredients like iodine, iron, and calcium, which are problematic for Hashimoto's patients. A general multivitamin could easily contain an excessive amount of iodine or disrupt the absorption of your medication. Selecting a thyroid-friendly multivitamin, free of high-dose iodine, iron, and calcium, is often a better choice, with careful timing around your medication still necessary.

Supplement Interactions with Levothyroxine


Supplement	Interaction with Levothyroxine	Recommendation
Iodine	Can worsen autoimmune attack and thyroid dysfunction.	Avoid unless directed by a doctor for diagnosed deficiency.
Calcium	Binds to medication in the gut, reducing absorption.	Separate intake by at least 4 hours.
Iron	Binds to medication, preventing absorption.	Separate intake by at least 4 hours.
Biotin	Interferes with lab tests, causing false readings.	Inform doctor and stop 2-3 days before testing.
Soy	May interfere with medication absorption.	Separate intake by at least 4 hours from medication.

Conclusion: Always Consult Your Healthcare Provider

Managing Hashimoto's is a personalized process. While this information can help you understand potential risks, it is not a substitute for professional medical advice. Always consult your endocrinologist or a thyroid-savvy healthcare provider before starting or stopping any vitamin or supplement, including herbal remedies or over-the-counter formulas. They can help you determine the appropriate course of action, taking into account your specific lab results, medication regimen, and overall health status. For more information on Hashimoto's, visit the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Frequently Asked Questions

You should be very cautious with standard multivitamins, as they often contain ingredients like iodine, iron, and calcium, which can interfere with thyroid medication or worsen your condition. It is best to choose a thyroid-friendly multivitamin specifically formulated without these problematic ingredients or to take them at a separate time from your medication, but always consult your doctor.

To ensure accurate lab results, the American Thyroid Association advises stopping high-dose biotin supplements at least 48 to 72 hours (2 to 3 days) before your thyroid function test. You should also inform your doctor that you were taking it.

High doses of iodine can aggravate the autoimmune attack on the thyroid gland in susceptible individuals. While iodine is essential for hormone production, excessive amounts can suppress thyroid function and trigger autoimmune flares, worsening Hashimoto's over time.

If you need calcium or iron, you can take supplements, but you must time them correctly. Both minerals interfere with the absorption of thyroid medication, so they should be taken at least four hours apart from your prescribed medicine.

These supplements are unregulated and can contain variable amounts of animal thyroid hormones. Taking them can cause dangerous imbalances in your hormone levels and interfere with your prescribed medication, potentially causing serious health problems.

While individual needs vary, some nutrients like selenium (in appropriate doses), zinc, and vitamin D may be beneficial. However, even with these, you should discuss supplementation with your doctor to ensure proper dosing and check for potential interactions.

Kelp supplements, which contain high amounts of concentrated iodine, should be avoided. While small amounts of iodine from food sources are typically fine, it's best for Hashimoto's patients to limit their intake of seaweed, kelp, and other very high-iodine foods to avoid over-stimulating the thyroid.