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
How to take it
Interactions
With medications
- laboratory immunoassays (troponin, thyroid function, hCG, hormone panels)
Biotin above about 5 mg/day distorts biotin-streptavidin based assays — it can hide a heart attack on a troponin test or mimic Graves' disease on thyroid results. stop biotin 48-72 hours before any blood draw and tell whoever orders the test
- carbamazepine, phenytoin and valproate
Long-term anticonvulsant therapy lowers biotin status. no action needed for most people; worth knowing if deficiency symptoms appear
Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.
Frequently asked questions
Does biotin work for hair growth?
Not if you are not deficient — the evidence is limited. The case for biotin rests on reports in people with biotin deficiency or rare metabolic defects; no placebo-controlled trial shows biotin improves hair in healthy people.
Does biotin strengthen brittle nails?
Weakly at best — the evidence is limited. Three small uncontrolled studies reported thicker nails with 2.5 mg/day of biotin, but there is no placebo-controlled replication and fewer than 100 people studied in total.
Can biotin affect blood test results?
Yes, and this is biotin's real danger. Biotin at about 5 mg/day and up can falsify troponin, thyroid and hormone tests, which has led to missed heart attacks; stop biotin 48–72 hours before blood tests and tell the lab.
Is high-dose biotin safe?
Biotin has no known direct toxicity even at 300 mg/day. The hazard is lab-test interference, so always tell whoever orders your tests that you take biotin, especially in an emergency.
Scientific references
Where to buy
NOW Foods, Biotin, 5,000 mcg, 120 Veg Capsules
Ships to 180+ countries · welcome discount for new customers
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Related in Joints & skin
- Curcumin (Turmeric extract) Moderate evidence
- Collagen Peptides Moderate evidence
- Glucosamine Limited evidence
- MSM (Methylsulfonylmethane) Limited evidence
- Chondroitin Sulfate Moderate evidence
- Hyaluronic Acid Limited evidence