Quick answer

NIH says biotin has not been shown to cause harm, no upper limit is set, and studies giving 10 to 50 mg a day found no adverse effects. The real problem is different: biotin above the recommended intake can make some blood tests read falsely high or falsely low.^1,2,3

Key facts

Wrong results have been reported in thyroid, reproductive hormone and heart tests, and in tests that measure some medicines.⁴
In six healthy adults, 10 mg a day for a week gave wrong results on 9 of 23 tests that use biotin.⁵
NIH's biotin fact sheets do not list weight gain or skin breakouts among its effects.^1,2
Taking some anticonvulsants for a year or more can lower biotin levels.¹

Effects on the body

No upper limit has been set for biotin, because there is no evidence in humans that it is toxic at high intakes. Studies giving 10 to 50 mg a day found no adverse effects, and people with a rare inherited condition that affects biotin have taken up to 200 mg a day by mouth without signs of toxicity. The main known risk of high intakes is wrong lab test results.^2,6

People often ask about weight gain, acne or other skin changes. Neither NIH fact sheet lists them, and both say biotin has not been shown to cause harm. If your skin or anything else changes after you start a supplement, stop it and ask your doctor.^1,2

The real risk: wrong lab test results

Many lab tests use biotin as part of how they work, because it binds tightly to proteins such as streptavidin. Extra biotin in a blood sample can upset that binding and shift the result up or down, depending on the test's design.^3,5

Biotin above the recommended intake can make some lab tests read falsely high or falsely low, depending on how the test is built. Wrong results can lead to the wrong treatment or to a missed or mistaken diagnosis.^2,3

In six healthy adults who took 10 mg of biotin a day for a week, 9 of 23 lab tests built with biotin gave wrong results, some falsely high and some falsely low.⁵

The tests most at risk include thyroid and reproductive hormone tests, heart tests such as troponin, and tests that measure some immune-suppressing medicines. Since 2016, 92 cases of suspected biotin interference have been reported to FDA.⁴

The direction of the error matters. A falsely high result can suggest a problem that is not there, as when thyroid tests seemed to show an overactive thyroid. A falsely low result can hide a real one, as when a troponin test missed heart damage.^2,5

Case reports describe thyroid test results that falsely suggested Graves' disease or a severely overactive thyroid in people taking 10 to 300 mg of biotin a day.²

FDA has reported that a patient taking high-dose biotin died after a troponin test, used to help diagnose a heart attack, gave a falsely low result. FDA continues to receive reports of falsely low troponin results caused by biotin.^2,7

What to do before a blood test

Tell the doctor who orders the test, and the lab, that you take biotin and how much³
Ask whether to pause biotin before the test, and for how long, since the level that upsets a test varies by test and by maker⁸
If a result does not fit how you feel, mention biotin again: FDA advises clinicians to consider biotin when results do not match the clinical picture²
Remember biotin you may not think of, in multivitamins, prenatal vitamins and hair, skin and nail products³

Medicines, and who should ask first

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.^2,9

On the medicine's label

Your doctor may want to check on you

In a study of 264 people with epilepsy, taking anticonvulsants such as carbamazepine, phenytoin, phenobarbital or primidone for a year or more was linked to lower biotin levels. These medicines may speed up the breakdown of biotin and reduce its absorption.^1,2

Reported in studies

Ask first if you take a thyroid medicine or an anticonvulsant
Ask first if you are pregnant or breastfeeding
Ask first if you have a heart condition and may need urgent blood tests, since a falsely low troponin result can delay care⁷

Questions people ask

Does biotin cause acne?

NIH's biotin fact sheets do not list acne as an effect, and we found no controlled trial showing that it does. If your skin changes after you start any supplement, stop it and ask your doctor.²

Does biotin cause weight gain?

Weight gain is not among the effects NIH lists, and NIH says biotin has not been shown to cause any harm.¹

Can I take biotin every day?

Daily biotin at or near the 30 mcg adult need is ordinary nutrition. At high daily doses no toxic effect has been found, but blood tests can be affected for as long as you keep taking it, so tell your doctor before any test.^2,3

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Sources

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