Biotin, also called vitamin B7 (and historically vitamin H), is a water-soluble B vitamin. The body needs it as a cofactor for a small set of carboxylase enzymes involved in making fatty acids, making glucose and breaking down some amino acids. Adults need very little: the US adequate intake is 30 µg per day, and true deficiency is rare in people who eat a normal diet.
Biotin is heavily marketed for hair, skin and nails, often in doses hundreds of times higher than that intake. For anyone who tracks bloodwork, the single most important fact is not a benefit but a lab problem: the FDA has warned (2017, updated 2019) that biotin in the blood can make many common immunoassays read falsely high or falsely low, including troponin, thyroid tests and hormone tests such as testosterone.
This page summarizes what the National Academies’ dietary reference report, clinical trials, laboratory studies and the FDA report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Class | Water-soluble B vitamin (vitamin B7) |
| Formula | C₁₀H₁₆N₂O₃S, 244.31 g/mol |
| Adult adequate intake (AI) | 30 µg/day; 35 µg/day during lactation |
| Upper limit (UL) | None set; data insufficient |
| Common supplement amounts | FDA is aware of many products with 20 mg, some with up to 100 mg per pill |
| Absorption | Essentially complete, even at pharmacologic oral doses |
| Half-life (published reports) | About 1.8 h after 600 µg; up to 18.8 h after a single 300 mg dose |
| High-dose MS drug (MD1003) | EU application withdrawn in 2017; failed its phase 3 trial (SPI2) in 2020 |
| Key safety issue | Interference with biotin-streptavidin lab tests (FDA safety communication, 2017 and 2019) |
What it is
Biotin is a small sulfur-containing molecule, 5-[(3aS,4S,6aR)-2-oxo-1,3,3a,4,6,6a-hexahydrothieno[3,4-d]imidazol-4-yl]pentanoic acid, with the formula C₁₀H₁₆N₂O₃S (PubChem). It was first described in 1927, but it took nearly 40 more years to be fully recognized as a vitamin (IOM 1998).
Its job is to act as a covalently bound cofactor for carboxylases. The enzyme holocarboxylase synthetase attaches biotin to each carboxylase, turning it from an inactive into an active enzyme (Mock, J Nutr 2017). The main enzymes are:
| Enzyme | Main role |
|---|---|
| Acetyl-CoA carboxylase (ACC1 and ACC2) | Forms malonyl-CoA, the starting point for fatty acid synthesis |
| Pyruvate carboxylase | Forms oxaloacetate, needed for making glucose (gluconeogenesis) |
| Methylcrotonyl-CoA carboxylase | Breakdown of the amino acid leucine |
| Propionyl-CoA carboxylase | Breakdown of some amino acids and odd-chain fatty acids |
When these enzymes break down, the enzyme biotinidase frees the biotin so it can be reused (IOM 1998).
How it behaves in the body
Most biotin in food is bound to protein. Biotin is widespread in foods but at very different concentrations: liver contains about 100 µg per 100 g, while fruits and most meats contain about 1 µg per 100 g (IOM 1998). Avidin, a protein found in raw egg white, binds biotin in the small intestine and prevents its absorption.
Oral biotin is very well absorbed. In a crossover study, 6 healthy adults took oral or intravenous biotin at several doses; urinary recovery suggested about 100% bioavailability even for the largest oral doses (Zempleni & Mock, AJCN 1999). Biotin and its main metabolites, bisnorbiotin and biotin sulfoxide, appear in urine and plasma in a ratio of roughly 3:2:1 (IOM 1998).
How long biotin stays in the blood depends heavily on dose:
| Finding | Source |
|---|---|
| Half-life about 1.8 h after a 600 µg dose; up to 18.8 h after a single 300 mg dose | Studies summarized by Li et al., JAMA 2017 |
| Peak blood levels 2–4 h after single doses of 5–150 mg (8 volunteers, 2 per dose) | Kabiri et al., J Clin Lab Anal 2021 |
| Biotin still above 50 ng/mL 24 h after a single dose in 5 of those 8 volunteers | Kabiri et al. 2021 |
| Mean biotin above 3,600 pg/mL (the assay ceiling) after 7 days of 10 mg/day, back to baseline 7 days after stopping | Li et al., JAMA 2017 |
These numbers matter mainly for lab testing, covered below.
Dietary intake reference values
The Institute of Medicine (now the National Academy of Medicine) set an Adequate Intake rather than a Recommended Dietary Allowance, because the evidence was too thin to estimate an average requirement. The adult AI of 30 µg/day was extrapolated from intake in breastfed infants (IOM 1998).
| Life stage | AI (µg/day) |
|---|---|
| 0–6 months | 5 |
| 7–12 months | 6 |
| 1–3 years | 8 |
| 4–8 years | 12 |
| 9–13 years | 20 |
| 14–18 years | 25 |
| Adults 19 and older (men and women) | 30 |
| Pregnancy | 30 |
| Lactation | 35 |
The report found no reported adverse effects of biotin in humans or animals and set no Tolerable Upper Intake Level. It noted that daily oral doses up to 200 mg had been used without reported toxicity in people with biotin-responsive inherited disorders (IOM 1998). That report predates the recognition of lab test interference, which is now the main practical risk of high doses.
Estimated intakes from diet are around 35–70 µg/day in Western populations, above the AI (Patel et al., Skin Appendage Disord 2017). The NIH Office of Dietary Supplements fact sheet on biotin covers the same reference values; we cite the underlying National Academies report here.
Deficiency
Frank biotin deficiency is rare. The well-documented cases fall into a few groups (Mock, J Nutr 2017; IOM 1998):
- long-term intravenous feeding (parenteral nutrition) without added biotin;
- eating large amounts of raw egg white for long periods;
- inherited disorders that waste biotin, mainly biotinidase deficiency and holocarboxylase synthetase deficiency.
People on dialysis may also need more biotin (IOM 1998).
In adults, the classic signs are:
- thinning hair, often with loss of hair color;
- a red, scaly rash around the eyes, nose and mouth;
- neurological symptoms such as depression, lethargy, hallucinations and tingling in the limbs.
Infants on biotin-free intravenous feeding developed symptoms within 3–6 months. In raw egg white feeding studies, urinary 3-hydroxyisovaleric acid, a leucine breakdown product that builds up when one biotin-dependent enzyme slows, rose abnormally in all 10 volunteers by day 14 (IOM 1998).
Pregnancy is the one setting where marginal deficiency may be common. Studies cited by Mock found increased 3-hydroxyisovaleric acid excretion in a substantial share of healthy pregnant women. In third-trimester women eating a controlled diet of about 60 µg/day (twice the AI), excretion was still higher than in controls. Marginal deficiency is teratogenic in mice, but whether it causes birth defects in humans is unproven (Mock, J Nutr 2017).
What the research shows
Hair and nails in people without deficiency
Biotin’s reputation for hair and nails comes largely from the fact that deficiency causes hair loss and rash. That does not mean extra biotin helps people who already have enough.
A systematic review found 18 reported cases of biotin use for hair or nail changes (Patel et al., Skin Appendage Disord 2017):
- every patient had an underlying cause of poor hair or nail growth;
- 10 of 18 had an inherited enzyme deficiency (biotinidase or holocarboxylase synthetase);
- 3 had uncombable hair syndrome and 3 had brittle nail syndrome;
- there were no randomized controlled trials in healthy people.
The authors concluded that biotin has no proven efficacy for hair and nail growth in healthy individuals.
For brittle nails specifically, the evidence is small and uncontrolled. A scanning electron microscopy study found that nail thickness increased by 25% in 8 patients with brittle nails measured before and after biotin, and by 7% in a second group of 14 (Colombo et al., J Am Acad Dermatol 1990). A later review judged the results promising but called for larger controlled trials (Lipner & Scher, J Dermatolog Treat 2018).
About “biotin for hair growth.” The evidence is limited to case reports in people with a deficiency or a specific hair or nail disorder, and to small uncontrolled studies of brittle nails. No randomized trial has shown that biotin makes hair grow in people with normal biotin status.
High-dose biotin in progressive multiple sclerosis
A pharmaceutical-grade high-dose biotin product, MD1003, was tested in progressive multiple sclerosis (MS) at 100 mg three times daily (300 mg/day), about 10,000 times the AI. The idea was that it might boost energy production in damaged nerve fibers and support myelin repair (Mock, J Nutr 2017).
| Trial | Design | Primary endpoint result |
|---|---|---|
| MS-SPI (Tourbah et al., Mult Scler 2016) | 154 patients, EDSS 4.5–7; 12 months MD1003 (n = 103) vs placebo (n = 51) | Disability improvement in 12.6% vs 0% (p = 0.005) |
| SPI2 (Cree et al., Lancet Neurol 2020) | 642 patients in 13 countries, EDSS 3.5–6.5; MD1003 (n = 326) vs placebo (n = 316) | Improvement in 12% vs 9%; odds ratio 1.35 (95% CI 0.81–2.26), not significant |
The smaller MS-SPI trial was positive. The larger phase 3 SPI2 trial was not. Its authors concluded that MD1003 “cannot be recommended” for progressive MS, citing both the lack of benefit and the risk of harm from lab test interference. SPI2 was funded by the manufacturer, MedDay Pharmaceuticals.
A meta-analysis pooled three randomized trials (889 patients). In progressive MS (2 trials, 796 patients), composite disability improvement did not differ significantly from placebo (relative risk 2.87, 95% CI 0.29–28.40). Lab test interference occurred in 31 of 662 (4.7%) biotin-treated patients and none on placebo (Espiritu & Remalante-Rayco, Mult Scler Relat Disord 2021).
In Europe, MedDay withdrew its marketing application for MD1003 (as Qizenday) in November 2017. The EMA’s committee had provisionally concluded that the effectiveness data were not robust enough and that the benefits did not outweigh the risks (EMA).
Side effects and risks
Direct toxicity
Biotin itself has low direct toxicity in the available data. The National Academies found no reported adverse effects (IOM 1998). In SPI2, treatment-emergent adverse events occurred in 84% of the biotin group and 85% of the placebo group, and serious adverse events in 26% of each (Cree et al. 2020). The main documented harm of high doses is indirect: wrong lab results.
The FDA warning on lab test interference
On November 28, 2017, the FDA issued a safety communication warning that biotin can “significantly interfere” with certain lab tests and cause incorrect results that may go undetected (FDA 2017). It updated the warning on November 5, 2019 (FDA 2019). Key points:
- Biotin can cause falsely high or falsely low results, depending on the test.
- The FDA received a report that a patient taking high levels of biotin died after falsely low troponin results on a troponin test known to be affected.
- Many tests are potentially affected, “including but not limited to” cardiovascular tests and hormone tests.
- Many hair, skin and nail supplements contain up to 650 times the recommended daily intake. Physicians may recommend up to 300 mg/day for conditions such as MS.
- The 2019 update said some test makers had fixed the problem, others had not, and the FDA kept receiving reports of falsely low troponin results. It posted a list of troponin assays still subject to biotin interference.
- Specimens from people on up to 300 mg/day may contain up to 1,200 ng/mL of biotin.
- The FDA said there is not enough information to know whether stopping biotin for any particular number of hours before a test prevents incorrect results.
Why biotin breaks these tests
Many automated immunoassays use the extremely tight bond between biotin and the protein streptavidin to capture the test complex. Extra biotin in the patient’s blood takes up the streptavidin binding sites. What happens next depends on the assay format (Mock, J Nutr 2017; Stieglitz et al., J Endocr Soc 2018; Kabiri et al., J Clin Lab Anal 2021):
| Assay format | Typically used for | Effect of excess biotin |
|---|---|---|
| Sandwich (immunometric) | Large molecules: TSH, troponin, FSH, LH, PTH, prolactin | Falsely low |
| Competitive | Small molecules: testosterone, estradiol, cortisol, T4, T3 | Falsely high |
Whether a given test is affected depends on the manufacturer and the specific assay design, not just on the analyte. Mass spectrometry (LC-MS/MS) methods do not use biotin-streptavidin capture and are not affected (Stieglitz et al. 2018).
Concrete examples
Troponin (heart attack diagnosis). In spiking experiments on Roche Elecsys assays, troponin T and TSH were the most sensitive, showing interference at biotin concentrations as low as 15.6–31.3 ng/mL. At 500 ng/mL or more, all tested assays showed significant interference (Trambas et al., Ann Clin Biochem 2018). How common this is in practice:
| Population | Biotin level found | Source |
|---|---|---|
| 1,442 emergency department patients | 7.4% at or above 10 ng/mL, the lowest known interference threshold for Roche immunoassays | Katzman et al., Clin Biochem 2018 |
| 1,944 surveyed outpatients | 7.7% reported taking biotin | Katzman et al. 2018 |
| 797 emergency patients with suspected acute coronary syndrome | 0.13% above 20 ng/mL, the interference threshold of a newer troponin T assay | Mumma et al., Clin Chem Lab Med 2020 |
For that newer troponin T assay, Mumma et al. estimated the risk of a missed heart attack from biotin at about 0.026% for a first sample. The risk is low per test, but the FDA’s death report shows what is at stake.
Thyroid tests. Biotin pushes results toward a false picture of hyperthyroidism: TSH (sandwich) reads low while T4 and T3 (competitive) read high.
- In 6 healthy adults taking 10 mg/day for 7 days, interference appeared in 9 of 23 biotin-based assays and none of 14 non-biotin assays. One TSH assay dropped below 0.15 mU/L, low enough to suggest thyrotoxicosis in people with normal thyroid function. Several free and total T3 and T4 assays read falsely high (Li et al., JAMA 2017).
- In the MS-SPI trial, 6 patients on high-dose biotin were recorded as having hyperthyroidism. In 5 of them it was judged to be lab interference rather than true disease (Tourbah et al. 2016).
Testosterone, FSH and LH. A 48-year-old woman taking 5 mg/day of biotin was investigated for a possible testosterone-producing tumor, and a surgical procedure was scheduled (Stieglitz et al., J Endocr Soc 2018):
| Test | Biotin-sensitive immunoassay | Biotin-free method |
|---|---|---|
| Total testosterone (reference 6–77 ng/dL) | 232 ng/dL at first visit | 15 ng/dL by LC-MS/MS (measured later, while still on biotin) |
| Morning cortisol | 115 µg/dL (very high) | Urine and saliva cortisol normal by LC-MS/MS |
| TSH | 0.06 mIU/mL (low) | 1.1 mIU/mL on a non-biotin assay |
| FSH and LH | Lower than expected for her perimenopausal state | — |
Her measured blood biotin was 38 ng/mL, and the abnormal results resolved after she stopped biotin. Her TSH immunoassay was still abnormal 2 weeks after stopping.
In 23 plasma samples from MS patients and volunteers on high-dose biotin (biotin 31.7–1,160 µg/L), most results on Roche hormone assays, including FSH and LH, were abnormal. They normalized after the biotin was removed from the samples in the lab (Piketty et al., Clin Chem Lab Med 2017). A study of 59 Roche assays labeled as interference-suppressed found that the competitive assays as a group, which included testosterone, estradiol and progesterone, read on average 20.8% higher with just 10 ng/mL of added biotin. Sandwich assays in that study, including FSH, LH and SHBG, did not always behave as predicted (Kabiri et al., J Clin Lab Anal 2021).
Why this matters if you track your bloodwork
Panels used to monitor testosterone therapy or other hormone use can include testosterone, estradiol, LH, FSH and TSH, all of which appear in the studies above. On an affected assay, a hair, skin and nail product can produce results that look plausible but are wrong, for example:
- testosterone or estradiol reading higher than it really is;
- LH and FSH reading lower than they really are, which can look like suppression;
- a low TSH with high T3 and T4, which can look like hyperthyroidism;
- a falsely low troponin during chest pain.
The FDA advises patients to tell their clinician about biotin, including in multivitamins and hair, skin and nail products. It advises clinicians to tell the lab and to consider biotin when a result does not fit the clinical picture (FDA 2019). Guidance on how long to stop before testing differs:
- The FDA says the data are insufficient to set a safe waiting time.
- Li et al. suggested that stopping for about a week, as in their study, may be advisable (Li et al., JAMA 2017).
- In single-dose volunteers, biotin was still elevated 24 h later, longer than the 8 h minimum stated for some Roche assays (Kabiri et al. 2021).
Another option, when available, is a method that does not use biotin, such as LC-MS/MS for testosterone.
For related micronutrient pages, see vitamin B12 and zinc.
Key takeaways
- An essential B vitamin needed in tiny amounts. The adult adequate intake is 30 µg/day (35 µg/day when breastfeeding), and most diets supply that.
- Deficiency is rare. It occurs mainly with biotin-free intravenous feeding, prolonged raw egg white intake and inherited disorders such as biotinidase deficiency. Pregnancy may cause a marginal deficiency.
- No good evidence for hair or nails in healthy people. Reported benefits come from people with a deficiency or specific disorders, plus small uncontrolled brittle-nail studies.
- High-dose biotin failed in progressive MS. The phase 3 SPI2 trial (642 patients, 300 mg/day) showed no significant benefit, and the EU application was withdrawn.
- The main risk is wrong lab results. The FDA warns that biotin can make immunoassays read falsely high or low, including troponin, thyroid tests, testosterone, estradiol, FSH and LH. One death after a falsely low troponin result has been reported.
- Biotin use belongs on the lab requisition. The FDA asks patients to tell clinicians about biotin-containing products and clinicians to tell the lab, and to suspect biotin when results do not fit the clinical picture.
Sources
- Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Chapter 11: Biotin. Washington, DC: National Academies Press; 1998. doi:10.17226/6015. NAP.
- Food and Drug Administration. The FDA warns that biotin may interfere with lab tests: FDA safety communication. November 28, 2017. FDA.
- Food and Drug Administration. UPDATE: The FDA warns that biotin may interfere with lab tests: FDA safety communication. November 5, 2019. FDA.
- National Center for Biotechnology Information. Biotin (CID 171548). PubChem Compound Database. PubChem.
- Mock DM. Biotin: from nutrition to therapeutics. J Nutr. 2017;147(8):1487–1492. PubMed.
- Zempleni J, Mock DM. Bioavailability of biotin given orally to humans in pharmacologic doses. Am J Clin Nutr. 1999;69(3):504–508. PubMed.
- Patel DP, Swink SM, Castelo-Soccio L. A review of the use of biotin for hair loss. Skin Appendage Disord. 2017;3(3):166–169. PubMed.
- Colombo VE, Gerber F, Bronhofer M, et al. Treatment of brittle fingernails and onychoschizia with biotin: scanning electron microscopy. J Am Acad Dermatol. 1990;23(6 Pt 1):1127–1132. PubMed.
- Lipner SR, Scher RK. Biotin for the treatment of nail disease: what is the evidence? J Dermatolog Treat. 2018;29(4):411–414. PubMed.
- Tourbah A, Lebrun-Frenay C, Edan G, et al. MD1003 (high-dose biotin) for the treatment of progressive multiple sclerosis: a randomised, double-blind, placebo-controlled study. Mult Scler. 2016;22(13):1719–1731. PubMed.
- Cree BAC, Cutter G, Wolinsky JS, et al. Safety and efficacy of MD1003 (high-dose biotin) in patients with progressive multiple sclerosis (SPI2): a randomised, double-blind, placebo-controlled, phase 3 trial. Lancet Neurol. 2020;19(12):988–997. PubMed.
- Espiritu AI, Remalante-Rayco PPM. High-dose biotin for multiple sclerosis: a systematic review and meta-analyses of randomized controlled trials. Mult Scler Relat Disord. 2021;55:103159. PubMed.
- European Medicines Agency. Qizenday (biotin): withdrawal of the marketing authorisation application. EMEA/H/C/004153. EMA.
- Li D, Radulescu A, Shrestha RT, et al. Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA. 2017;318(12):1150–1160. PubMed.
- Trambas C, Lu Z, Yen T, Sikaris K. Characterization of the scope and magnitude of biotin interference in susceptible Roche Elecsys competitive and sandwich immunoassays. Ann Clin Biochem. 2018;55(2):205–215. PubMed.
- Kabiri P, Weiskirchen R, van Helden J. The biotin interference within interference suppressed immunoassays. J Clin Lab Anal. 2021;35(9):e23940. PubMed.
- Stieglitz HM, Korpi-Steiner N, Katzman B, et al. Suspected testosterone-producing tumor in a patient taking biotin supplements. J Endocr Soc. 2018;2(6):563–569. PubMed.
- Piketty ML, Prie D, Sedel F, et al. High-dose biotin therapy leading to false biochemical endocrine profiles: validation of a simple method to overcome biotin interference. Clin Chem Lab Med. 2017;55(6):817–825. PubMed.
- Katzman BM, Lueke AJ, Donato LJ, et al. Prevalence of biotin supplement usage in outpatients and plasma biotin concentrations in patients presenting to the emergency department. Clin Biochem. 2018;60:11–16. PubMed.
- Mumma B, Diercks D, Twerenbold R, et al. Clinical risk assessment of biotin interference with a high-sensitivity cardiac troponin T assay. Clin Chem Lab Med. 2020;58(11):1931–1940. PubMed.