Biotin is everywhere in the wellness aisle: in gummies, powders, and "hair-skin-nails" supplements that promise lusher strands and stronger tips in a matter of weeks. The premise is simple and seductive, but the science behind it is less settled than the marketing suggests.
In a recent video, Dr. Dana Stern, the board-certified dermatologist behind Dr. Dana Nail Care, explained why she no longer recommends biotin supplementation to her patients. Below, we summarize her perspective alongside the published evidence, so you can make an informed choice.
The short version: Biotin is a water-soluble B vitamin most healthy adults already get from food. High-quality evidence that supplementing it improves hair or nail growth in people without a deficiency is limited. And in 2016, The New England Journal of Medicine published a letter describing a real clinical problem — biotin interference — in which high-dose biotin can distort common blood tests, including thyroid and cardiac panels.
What Is Biotin?
Biotin, or vitamin B7, is a water-soluble B vitamin your body uses to metabolize fats, carbohydrates, and proteins. The National Institutes of Health Office of Dietary Supplements sets the adequate daily intake for adults at 30 micrograms (mcg). Most commercial hair-and-nail supplements contain 5,000 to 10,000 mcg per dose — hundreds of times the daily requirement.
According to the NIH, biotin deficiency is very rare in the United States because most people get enough from a varied diet. It is found in egg yolks, salmon, almonds, sunflower seeds, sweet potatoes, spinach, avocado, and organ meats. When deficiency does occur — typically in specific medical situations like long-term anticonvulsant use, certain genetic conditions, or after bariatric surgery — it can cause hair thinning, brittle nails, and skin changes. Correcting that kind of deficiency is a different situation from supplementing in someone whose diet is already sufficient.
Does Biotin Help Hair and Nail Growth?
The honest answer, based on the published literature: for healthy adults without a biotin deficiency, the evidence is limited.
A widely cited 2018 review in the Journal of the American Academy of Dermatology, Rethinking biotin therapy for hair, nail, and skin disorders, examined the available studies and concluded there is no sufficient high-quality evidence to recommend biotin supplementation for healthy people. A 2024 review in the Journal of Clinical and Aesthetic Dermatology reached the same conclusion. The American Academy of Dermatology has also published on this directly, noting biotin supplementation has not been shown to benefit normal, healthy hair.
Small, older studies did suggest oral biotin may improve brittle nails in some patients, which is why the supplement became popular in the first place. But those studies were small, not placebo-controlled, and have not been reproduced at scale. As Dr. Dana put it in her video, after reviewing the literature: "The studies simply weren't there."
The Risk Dr. Dana Highlights: Biotin Interference with Blood Tests
The reason Dr. Dana stopped recommending biotin is not that it is unsafe in the usual sense. It is that high-dose biotin can interfere with the chemistry of common laboratory tests.
In 2016, The New England Journal of Medicine published a letter titled Biotin Treatment Mimicking Graves' Disease, describing patients whose thyroid blood work was skewed — in some cases to the point of mimicking hyperthyroidism — because they were taking high doses of biotin. Many clinical immunoassays rely on a biotin-streptavidin binding system, and excess circulating biotin can falsely raise or lower a result depending on the test.
Since then, the U.S. Food and Drug Administration has issued multiple safety communications on biotin interference, with particular concern for troponin (used to diagnose heart attacks) and thyroid-function tests.
Does biotin affect thyroid tests? Yes. High-dose biotin can make TSH appear suppressed and free T4 appear elevated, a pattern that can mimic hyperthyroidism. When biotin is stopped and the labs are repeated, the numbers typically normalize within 24–48 hours.
When to stop biotin before a blood test. Most labs recommend discontinuing biotin supplements at least 48 to 72 hours before any blood draw; some assays require longer. If you take biotin, tell your physician and the phlebotomist before your draw.
How Much Biotin Is Too Much?
The NIH has not set a tolerable upper limit for biotin, because excess is excreted in urine. However, doses in the 5,000 to 10,000 mcg range — standard in hair-and-nail formulas — are well within the range that can trigger interference on common lab tests. There is no evidence that higher doses of biotin improve hair or nail outcomes in healthy adults.
What Supports Stronger Hair and Nails Instead
For healthy people who want stronger hair and nails, the more reliable path is not in a capsule. It starts with a protein-adequate diet (hair and nails are built from keratin), careful treatment of the nails themselves — gentle filing, avoiding at-home gel removal and acetone soaks, hands-off time between manicures — and an evaluation from a dermatologist when hair loss or persistent nail changes don't resolve with basic care. Underlying causes like thyroid disease, iron deficiency, or autoimmune conditions deserve a proper workup, not a supplement.
Explore Dr. Dana's dermatologist-developed nail care system →
FAQ
Is biotin bad for you? In food-sourced amounts, no. In high-dose supplement form, biotin is not acutely toxic, but it can interfere with common lab tests, including thyroid and cardiac assays.
Can you take too much biotin? The NIH has not set an upper limit, but high doses (5,000–10,000 mcg) can skew laboratory results.
Does biotin make your hair grow? For people without a biotin deficiency — which is most healthy adults — the evidence does not support a meaningful benefit.
Does biotin affect thyroid tests? Yes. High-dose biotin can distort TSH, free T4, and free T3 results. Stop biotin at least 72 hours before thyroid testing and tell your physician.
Is biotin good for nails? Some older, small studies suggested a possible benefit for brittle nails, but current dermatology reviews consider the evidence insufficient for healthy adults.
Sources cited in the article
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NIH Office of Dietary Supplements, Biotin — Health Professional Fact Sheet — ods.od.nih.gov
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Kummer S. et al., Biotin Treatment Mimicking Graves' Disease, New England Journal of Medicine, 2016 — nejm.org
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U.S. Food and Drug Administration, Biotin Interference with Troponin Lab Tests — Assays Subject to Biotin Interference — fda.gov
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Patel D.P., Swink S.M., Castelo-Soccio L., Rethinking biotin therapy for hair, nail, and skin disorders, Journal of the American Academy of Dermatology, 2018 — jaad.org
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Biotin for Hair Loss: Teasing Out the Evidence, Journal of Clinical and Aesthetic Dermatology, 2024 — PMC
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American Academy of Dermatology, Biotin supplementation for hair and nail health: Does it pass the test? — aad.org
