Last updated: September 2026 · Reading time: 6 minutes
Quick answer: High-dose biotin, the kind found in many hair, skin and nail supplements, can interfere with some blood tests and produce results that are falsely high or falsely low. Thyroid function tests and troponin (a test used to diagnose heart attacks) are the best-known examples. If you take a biotin supplement, tell your doctor or the person taking your blood, and ask whether you should pause it beforehand.
Why biotin affects blood tests
Many laboratory tests, called immunoassays, use the strong natural bond between biotin and a protein called streptavidin to capture and measure hormones and other markers. When there's a lot of extra biotin in the blood sample, it competes in that reaction and throws the measurement off. Depending on how the specific test is designed, the result can come out artificially high or artificially low.
The US Food and Drug Administration issued a safety warning about this in 2017, after reports of falsely low troponin results, and updated it in 2019. Laboratories in the UK are aware of the issue, and some ask about biotin before testing.
Which tests can be affected
- Thyroid tests: biotin can produce a falsely low TSH and falsely high free T4 and T3, a pattern that can look like an overactive thyroid when there isn't one.
- Troponin: can be falsely low, which is the most serious concern because it could delay recognition of a heart attack.
- Other hormone tests: some assays for reproductive hormones, cortisol, PTH and vitamin D can also be affected, depending on the laboratory's method.
Not every lab uses biotin-sensitive methods, and manufacturers have been redesigning tests to reduce the problem. That's why the safest step is simply to tell the lab.
Which doses matter
The adult requirement for biotin is tiny. EFSA sets an adequate intake of 40 micrograms (µg) a day. Interference is mainly linked to high-dose supplements, which often contain 5,000–10,000µg (5–10mg) per serving, more than 100 times the daily requirement. Standard multivitamins usually contain far less. Our Daily Multi Complex, for example, provides 25µg.
Check the biotin figure on any hair, skin and nail product you take, including ours, and mention it if it's in the milligram range.
What to do before a blood test
- Tell the clinician or phlebotomist that you take biotin, and at what dose.
- Ask whether to pause it. Many labs suggest stopping high-dose biotin for at least 48–72 hours before a test, and longer for very high doses. Follow your lab's or GP's advice.
- If a result doesn't fit how you feel, particularly a thyroid result, ask whether biotin could be a factor before any treatment decisions are made.
- In an emergency, tell the medical team about any supplements you take.
Never stop prescribed medication before a test without advice from your doctor.
Do you need high-dose biotin at all?
For most people, probably not. True biotin deficiency is rare, and the evidence that extra biotin helps hair in people who aren't deficient is weak. We cover that evidence in Biotin for hair growth: does it work? If hair shedding is your concern, iron and zinc status are often more relevant. See female hair loss: iron and zinc.
Related: Is biotin halal? and supplements and thyroid health.
Frequently asked questions
Can biotin affect thyroid test results?
Yes. High-dose biotin can make TSH look falsely low and free T4 falsely high on some test methods.
How long before a blood test should I stop biotin?
Many labs suggest at least 48–72 hours for high-dose biotin, but follow your GP's or lab's specific advice.
Does a normal multivitamin affect blood tests?
Standard multivitamins usually contain small amounts of biotin that are less likely to interfere, but it's still worth mentioning any supplements you take.
How much biotin is in hair supplements?
Many contain 5,000–10,000µg per serving, compared with a daily requirement of about 40µg.
Sensible-dose, halal approved daily nutrition.
Use code HALAL10 for 10% off. Shop Daily Multi Complex →
This article is for general information and isn't a substitute for medical advice. Always tell your healthcare team about supplements you take.
