vitamin · for hair thinning
Biotin
Biotin helps build keratin, the protein hair is made of.
Say that in clinical terms
Biotin is a cofactor for carboxylase enzymes involved in keratin protein synthesis. It supports hair follicle stem cell proliferation, improves hair shaft cortex structure, and reduces brittleness. Deficiency causes diffuse alopecia.
How strong is the research?
Two weeks of 5 mg a day did nothing for hair length or coverage in healthy men.
2 papers read, 1 against.
Who was studied: Almost all the evidence is in people with an inherited enzyme disorder that causes real biotin deficiency.
How much to take
daily
2500–5000 mcg
Allow 3-6 months for visible hair changes. Note: biotin can interfere with some lab tests (thyroid, troponin). Discontinue 48h before blood work.
Before you take it
- No Tolerable Upper Intake Level (UL) has been established by NIH ODS/FNB for biotin. The FNB concluded that no human toxicity from high biotin intake has been documented; doses up to 200 mg/day orally have been studied without adverse direct effects. No UL can be derived from current evidence.
- Biotin-streptavidin immunoassay interference: At supplemental doses of 5 mg (5,000 mcg) and above, biotin causes clinically significant false laboratory results in immunoassays using biotin-streptavidin capture technology. Affected tests include cardiac troponin (falsely LOW — the FDA received one patient death report from a missed cardiac diagnosis), TSH (falsely suppressed, mimicking thyrotoxicosis or falsely elevated), free T4, free T3, and sex hormone panels. The FDA issued safety communications in November 2017 and November 2019. Even a single 10 mg dose can interfere with thyroid function tests administered within 24 hours. Patients must disclose biotin use to clinicians before any blood draw and should wait at least 8 hours (up to 72 hours for some assays) after last dose before blood collection.
- Anticonvulsant-biotin depletion: Carbamazepine, primidone, phenytoin, and phenobarbital — after at least 1 year of treatment — significantly lower serum biotin levels by increasing biotin catabolism and inhibiting intestinal biotin absorption. Patients on these anticonvulsants may have higher biotin requirements.
- Raw egg white consumption depletes biotin: avidin in raw (not cooked) egg whites binds dietary biotin in the GI tract and prevents absorption. Sustained consumption of raw eggs can induce biotin deficiency.
When to take it
Best taken: morning
What we make of it
Eighteen case reports, and the authors themselves say the evidence is insufficient.
The detail
What we cite is a review of 18 individual case reports rather than a trial, and its own authors conclude there is not enough evidence to recommend biotin for healthy people. A stricter 2024 review found only three studies worth including at all.