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Biotin (Vitamin B7)
B vitamin popular for hair and nails. The honest verdict: only old, small, mostly uncontrolled trials support firmer brittle nails — there's no good evidence for hair growth unless you're deficient, and high doses skew lab tests.
What the evidence says
Biotin doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality meta-analyses and randomised trials published 1989–2026 with a typical study size of 70 participants.
Based on 37 studies · 4 meta-analyses · 19 RCTs · 4,799 total participants
Confidence
High confidenceBy outcome
Older uncontrolled trials suggest biotin firms brittle nails, but hair-growth evidence outside deficiency is thin and the large MS trials (SPI2) and most metas are unrelated to cosmetic use.
15 randomised trials
every one checked individually
Every randomised or controlled trial of Biotin indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
PubMed · as of Jul 2026
23 trials ongoing or recruiting · 67 completed on ClinicalTrials.gov
9 of the completed trials have posted results
Registered trials show research momentum for Biotin, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Biotin meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Authorised claims
“Biotin contributes to normal energy-yielding metabolism”
“Biotin contributes to normal functioning of the nervous system”
“Biotin contributes to normal macronutrient metabolism”
“Biotin contributes to normal psychological function”
“Biotin contributes to the maintenance of normal hair”
“Biotin contributes to the maintenance of normal mucous membranes”
“Biotin contributes to the maintenance of normal skin”
Not authorised by EFSA
“Biotin Necessary to maintain energy and general vitality”
“Biotin Necessary for healthy teeth, bones, hair, skin and nails”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Biotin (Vitamin B7) is a water-soluble B vitamin essential for fatty acid synthesis, gluconeogenesis, and amino acid metabolism. True deficiency is rare. Its strongest (though weak) evidence is for brittle nail syndrome, from old, small, largely uncontrolled studies.
Despite its reputation as a hair supplement, no trials show a hair benefit in people who aren't deficient. High-dose biotin can also interfere with some lab tests (thyroid, hormone, troponin): tell the clinician and the laboratory the exact product and amount, and follow their instructions for the test.
Supports protein building blocks of hair and nails
Essential for energy metabolism
How Biotin works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Safe at normal doses; may help prevent deficiency
High-dose biotin can make some lab tests (thyroid, troponin, hormones) read falsely high or low. Tell the lab and your doctor how much you take, and follow the lab's instructions for that test. This interaction is awaiting review by a qualified pharmacist and has not been assigned a severity. It is shown so you can raise it, not because its risk has been established. Ask a pharmacist or prescriber before combining, and do not stop or change prescribed medicines based on this notice.
May reduce biotin levels
Tip: Reduce dose
Biotin has an evidence score of 5/10 — moderate evidence based on 37 indexed studies, including 4 meta-analyses. B vitamin popular for hair and nails. The honest verdict: only old, small, mostly uncontrolled trials support firmer brittle nails — there's no good evidence for hair growth unless you're deficient, and high doses skew lab tests. Representative study: PMID 41124782.
The commonly studied dose of Biotin is 2500-5000mcg (2.5-5mg) for hair/nails. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Biotin is in the morning. Taking it with food is preferred. Biotin (vitamin B7) is a water-soluble B vitamin involved in carboxylase enzyme function for energy metabolism, gluconeogenesis, and keratin production.
Biotin has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. Reported side effects are uncommon and include acne (rare). Use caution if any of these apply to you: Known allergy or hypersensitivity to Biotin or related compounds; May interfere with lab test results (thyroid panels, troponin, hormone assays) — inform healthcare providers before blood tests.
Folic Acid
Too few graded studiesThe synthetic, fully oxidised form of vitamin B9 — the compound the neural-tube-defect prevention trials and food fortification actually used. It is NOT methylfolate: it needs dihydrofolate reductase to become active.
Vitamin C
Likely helpsHumans cannot synthesize this vitamin — required for collagen production, immune cell function, and iron absorption; athletes need more.
Vitamin B12
Likely helpsDrives nerve myelination, red blood cell formation, and DNA synthesis — deficiency is common in vegans, vegetarians, and older adults.
Vitamin D3
Probably helpsHormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
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Reviewed by Dr. Baher Al Hakim · Last reviewed May 2026 · evidence from 37 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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