Supplement analysis backed by scientific evidence · PT

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Limited evidenceJoints & skin

Biotin (Vitamin B7)

Biotin is sold everywhere for hair, skin and nails, and the evidence for that use in people without deficiency is close to nonexistent. Its most important real-world effect is dangerously distorting common laboratory tests.

What the science says

  • Improves hair growth or thickness in people without deficiency Limited evidence

    A dermatology review identified only a handful of case reports and uncontrolled series showing benefit, all in patients with an underlying biotin deficiency or inherited metabolic defect. There is no randomised placebo-controlled trial demonstrating that biotin improves hair in healthy people with normal biotin status — the entire market rests on deficiency case reports.

  • Strengthens brittle nails Limited evidence

    Three small uncontrolled studies from the 1980s and 1990s reported increased nail plate thickness with 2.5 mg/day biotin in women with brittle nails. No placebo-controlled replication exists, and the total evidence base is fewer than 100 subjects. This is the least-bad claim biotin has, and it is still weak.

  • Slows progression in progressive multiple sclerosis Limited evidence

    The phase 3 SPI2 trial randomised 642 patients with progressive MS to high-dose biotin (MD1003, 300 mg/day) or placebo and found no difference in confirmed disability improvement at 12 months. An earlier positive phase 3 signal did not replicate — this line of research is effectively closed.

  • Interferes with clinical laboratory immunoassays Strong evidence

    Supplemental biotin at 5-10 mg/day and above causes falsely high or falsely low results in streptavidin-biotin based immunoassays, notably troponin, TSH, free T4 and hormone panels. The FDA has issued safety communications after a reported death from a missed troponin elevation. Stop biotin at least 48-72 hours before blood tests and tell the lab.

Dosage & safety

Studied doseAdequate intake is 30 mcg/day for adults and is easily met from eggs, nuts, seeds, liver and legumes — deficiency on a normal diet is rare. Hair-and-nail supplements typically deliver 5,000-10,000 mcg (5-10 mg), roughly 150-300 times the adequate intake, with no evidence supporting the dose. Nail studies used 2.5 mg/day. The failed MS trials used 300 mg/day. There is no established benefit above nutritional intake in healthy adults.
SafetyNo known direct toxicity even at 300 mg/day, and no tolerable upper limit has been set. The genuine hazard is assay interference: biotin above ~5 mg/day can falsify troponin (risking a missed heart attack), thyroid function tests (mimicking Graves' disease), hCG, vitamin D and hormone assays. Stop biotin 48-72 hours before any blood draw and disclose use. Chronic anticonvulsant therapy (carbamazepine, phenytoin, valproate), long-term antibiotics and raw egg white consumption (avidin binds biotin) can lower biotin status. Requirements rise in pregnancy. Not restricted in sport.

Scientific references

Where to buy

NOW Foods, Biotin, 5,000 mcg, 120 Veg Capsules

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