Heavily marketed for hair, skin, and nails — but those claims still sit below the grading threshold. The clearest supported use is rare genetic biotin deficiency, while high-dose multiple sclerosis evidence is mixed. The clearest safety issue is lab-test interference, especially with thyroid and troponin assays.
What the research says
Each row is a different health effect. A means the support looks strongest, B likely helpful, C mixed or modest, and — not enough human evidence yet.
Papers are individual studies. Research reviews summarize evidence from multiple studies, such as systematic reviews and meta-analyses.
B · Likely helpful
B
Genetic biotin deficiency & inborn errors of metabolism
2 of 5 reviews positive. Therapeutic biotin (5–20 mg/day) corrects symptoms in biotinidase deficiency and inherited metabolic disorders. Standard of care after newborn screening.
13 papers · 5 research reviews
C · Mixed or limited evidence
C
Multiple sclerosis (high-dose 300 mg/day)
Reviews disagree. Early MS-SPI signal positive, but the larger SPI2 RCT was null on disability progression. High-dose biotin (300 mg/day) is not a typical supplement dose.
10 papers · 6 research reviews
— · Not enough human evidence yet
—
Hair growth & hair loss
5 papers, all flagged low-confidence. Most use combination hair/skin/nails products; effect size not isolatable to biotin. Strongest signal in deficient populations only.
5 papers · 1 research review
—
Nail strength & brittle nails
Only 2 papers — below the 5-paper threshold. Older small trials suggested benefit at 2.5 mg/day, but evidence has not accumulated.
2 papers
—
Skin health & dermatitis
5 papers, all low-confidence. Most are case reports of biotin-responsive seborrheic dermatitis in infants. No robust evidence in adult skin health.
5 papers · 1 research review
Safety
Safety is graded separately from benefits. Read these cautions first, especially if you take medication or have a medical condition.
⚠ ConcerningThe human evidence points to a meaningful reason for caution.
⚠
Lab test interference (thyroid, troponin, hormone assays)
High-dose biotin (≥5 mg/day) interferes with streptavidin-biotin immunoassays. Causes falsely low TSH (mimics Graves' disease) and falsely low troponin (risks missing heart attacks). FDA warning issued 2017.
17 papers · 5 research reviews
Quick facts
Dose, form and timing based on trials in the database.
Typical dose
300 mcg – 10 mg/day for OTC supplements; consumer hair/skin/nails products typically 1–10 mg/day. RDA is 30 mcg/day from food. Therapeutic doses for biotinidase deficiency are 5–20 mg/day; MS trials used 300 mg/day (vastly higher)
Best taken
With or without food — biotin is well-absorbed either way. Once-daily dosing is standard. Stop supplementation 24–72 hours before lab tests due to assay interference
Form
D-biotin is the only biologically active form and what every supplement contains. Be cautious of multi-ingredient hair/skin/nails products where biotin's contribution is unclear
Common side effects
None significant at typical doses. Biotin is water-soluble and excess is excreted in urine. No documented toxicity even at very high doses
Drug interactions
Anticonvulsants (phenytoin, carbamazepine, phenobarbital) reduce biotin levels with chronic use. Otherwise minimal drug interactions reported
Lab test interference
High-dose biotin (≥5 mg/day) interferes with thyroid hormone tests, troponin (a heart-attack marker), and many hormone tests that use streptavidin-biotin chemistry. Stop biotin 24–72 hours before testing — longer for very high doses. FDA warning issued November 2017
Marketing reality check
Most adults are not biotin-deficient. Hair, skin, and nail trials in non-deficient populations show inconsistent benefit. Combination hair/skin/nails products often include zinc, collagen, and other ingredients — biotin's specific contribution is rarely isolated
Quality-verified products
Products that pass third-party quality testing.
Product quality data coming soon
Product recommendations are being built from USP Verified, NSF Certified, and Labdoor test data. Products will only appear here after the supplement itself clears the evidence bar above — and only if the product passes third-party purity testing.
How we graded Biotin
Grades come from 42 unique research papers indexed from PubMed — including 1 meta-analysis, 5 systematic reviews, and 4 randomized trials; the rest are case series and single-arm trials in genetic disease populations. Each supplement is graded by health effect using a certainty × effect matrix applied across PubMed evidence per health effect. Cochrane reviews and high-quality systematic reviews carry the most weight. From abstract-only data, "high certainty" is rare — most A grades come from moderate certainty plus consistent meaningful-positive evidence. See Methodology for full detail.