Quick answer

Ask your pharmacist or doctor before combining. The levothyroxine label says biotin can make the thyroid blood tests used to check your dose read wrong, and tells patients to stop biotin for a time before testing. In one study of healthy adults taking biotin, 9 of 23 lab tests that use it gave wrong results.^1,2

Key facts

The levothyroxine label says biotin supplements can interfere with thyroid hormone tests built on biotin and streptavidin, giving wrong results.¹
NIH reports cases in which biotin made thyroid tests falsely suggest Graves' disease or a severely overactive thyroid.³
Your doctor orders lab tests to check your response to levothyroxine, so a distorted result can affect your treatment.^1,4
Biotin is in biotin-only products, B-complex supplements and many multivitamins, including prenatal vitamins.^5,6

Ask your pharmacist or doctor first

Biotin can distort the thyroid blood tests used to check and adjust a levothyroxine dose. The levothyroxine label says biotin supplements interfere with thyroid hormone tests built on biotin and streptavidin, which may give wrong results, and tells patients to stop biotin and biotin-containing supplements for a time before thyroid testing.^1,3

On the medicine's label

What is documented

The levothyroxine label covers biotin in three places. Its dosing section tells prescribers to ask whether patients take biotin or biotin-containing supplements. Its section on lab tests says biotin is known to interfere with thyroid hormone tests built on a biotin and streptavidin reaction, which may give wrong results. Its advice to patients repeats the instruction to stop biotin for a period before thyroid testing.¹

FDA describes the same problem across many lab tests: biotin levels above what the recommended daily intake produces can make tests that use biotin read falsely high or falsely low, depending on how the test is built.⁶

Why the test matters with levothyroxine

Levothyroxine replaces thyroid hormone, and the label says the dose is judged by periodic TSH and T4 tests along with how you feel. A TSH or T4 result skewed by biotin could make the dose look too high or too low when it is not.¹

NIH notes that wrong results from biotin can lead to inappropriate treatment or a misdiagnosis. In a small study of healthy adults taking high-dose biotin for a week, several tests that use biotin gave wrong results, including falsely low TSH, while tests built differently did not.^2,3

Where biotin can come from

Biotin is sold on its own and is also common in multivitamins, prenatal vitamins and products marketed for hair, skin and nails. Laboratory experts note that people may not realize they are taking it, so read the Supplement Facts panel of everything you use.^6,7

What to ask your pharmacist or doctor

Do any of my supplements contain biotin, and how much?
How long before my next thyroid blood test should I stop biotin?
Should the lab be told that I take biotin?
Could biotin explain a test result that does not match how I feel?

Bring the labels of everything you take to that conversation, including vitamins you think of as basic.

Questions people ask

Does biotin change how levothyroxine is absorbed?

The sources on this page do not describe biotin changing levothyroxine absorption; their concern is the blood test. That is not a finding either way, so ask your pharmacist.¹

Does the small amount of biotin in a multivitamin count?

The label's instruction covers biotin-containing supplements in general, not only high-dose biotin, and FDA says intakes above the recommended amount can affect some tests. Ask your doctor what to do before your next thyroid test.^1,6

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.