Biotin (vitamin B7): Evidence, Trial Doses & Interactions

About Biotin (vitamin B7)

A water-soluble B vitamin acting as the cofactor for carboxylase enzymes in fat and amino-acid metabolism. It is the central ingredient in the hair, skin and nail supplement category.

Biotin is a marketing triumph built on a genuine but narrow observation: people with true biotin deficiency lose hair and develop brittle nails and a rash, and correcting the deficiency resolves them. True deficiency is rare — it occurs in biotinidase deficiency, long-term anticonvulsant use, prolonged raw egg white consumption and some malabsorption states. In people who are not deficient, there is essentially no controlled evidence that biotin does anything for hair or nails, and a review of the literature found the supporting reports were almost all in people with an underlying deficiency or pathology. Meanwhile the high doses sold — 5,000 to 10,000 µg, against an Adequate Intake of 30 µg — cause a real clinical problem: they distort laboratory tests, including the troponin assay used to diagnose heart attacks.

Sold as

Capsule, Tablet, Gummy, High-dose "hair, skin and nails" formula, Component of B-complex

Also known as

Vitamin B7, Vitamin H, D-biotin

Regulation: No Tolerable Upper Intake Level exists — the IOM found no evidence of toxicity. The FDA has issued repeated safety communications about biotin interference with laboratory immunoassays, including falsely low troponin results that could lead to a missed heart attack diagnosis. Doses in retail products are commonly 100–300 times the Adequate Intake.

What the research used

The amounts, forms and durations published trials of Biotin (vitamin B7) actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

Studied for Adequate Intake, adults
30 µg
Moderate
An Adequate Intake, since there was insufficient data for an RDA. Typical diets supply 35–70 µg/day and deficiency is rare.
Studied for Typical "hair, skin and nails" product
5000–10000 µg
Not enough
Capsule or gummy, daily
170–330 times the Adequate Intake, with no controlled evidence of benefit in people who are not deficient — and enough to distort several common blood tests.
Studied for Brittle nail studies
2500 µg
Limited
Daily · 6 months
From small uncontrolled studies in the 1980s and 1990s reporting thicker nails. No adequately controlled trial has confirmed this.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.

Any time
Not enough
No timing has been tested. The one timing point that matters is clinical: stopping biotin for a period before blood tests, on the advice of the requesting clinician, to avoid assay interference.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Blood glucose response

Blood Sugar & Metabolic Health

Not enough evidence

Some small studies of biotin with chromium reported modest glucose effects in type 2 diabetes, but results are inconsistent and the combination makes it impossible to attribute anything to biotin alone.

Not enough evidence. Not enough human research to say anything useful yet.

View the 3 sources

Combination of chromium and biotin improves coronary risk factors in hypercholesterolemic type 2 diabetes mellitus: a placebo-controlled, double-blind randomized clinical trial.(opens in a new tab)
Randomised controlled trial · Journal of the cardiometabolic syndrome · 2007 · PMID 17684468
Biotin supplementation reduces plasma triacylglycerol and VLDL in type 2 diabetic patients and in nondiabetic subjects with hypertriglyceridemia.(opens in a new tab)
Randomised controlled trial · Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie · 2006 · PMID 16677798
Treatment of brittle nail with a hydroxypropyl chitosan-based lacquer, alone or in combination with oral biotin: A randomized, assessor-blinded trial.(opens in a new tab)
Randomised controlled trial · Dermatologic therapy · 2019 · PMID 31344296

Deep research mode adds each paper’s own conclusion and stated limitations.

Hair growth and strength

Hair Health

Not enough evidence

A systematic review found the published reports of biotin improving hair were almost entirely in people with an underlying deficiency or a specific pathology. There is no good controlled evidence that it helps hair growth or thickness in people whose biotin status is normal — which is nearly everyone buying it.

What may be going on: Biotin is a cofactor for carboxylases involved in fatty-acid synthesis, and keratin production depends on those pathways. Deficiency causes hair loss; adequacy plus more does not produce more hair.

Not enough evidence. Not enough human research to say anything useful yet.

View the 3 sources

Efficacy of 5% topical minoxidil versus 5 mg oral biotin versus topical minoxidil and oral biotin on hair growth in men: randomized, crossover, clinical trial.(opens in a new tab)
Randomised controlled trial · Anais brasileiros de dermatologia · 2024 · PMID 38688776
Treatment of brittle nail with a hydroxypropyl chitosan-based lacquer, alone or in combination with oral biotin: A randomized, assessor-blinded trial.(opens in a new tab)
Randomised controlled trial · Dermatologic therapy · 2019 · PMID 31344296
Efficacy of intramuscular injections of biotin and dexpanthenol in the treatment of diffuse hair loss: A randomized, double-blind controlled study comparing two brands.(opens in a new tab)
Randomised controlled trial · Dermatologic therapy · 2022 · PMID 35791704

Deep research mode adds each paper’s own conclusion and stated limitations.

Skin structure and hydration

Skin Health

Not enough evidence

The scaly rash of biotin deficiency resolves with repletion. Beyond that, there is no controlled evidence that supplementation changes skin in people with adequate status.

Not enough evidence. Not enough human research to say anything useful yet.

View the 3 sources

A Collagen Supplement Improves Skin Hydration, Elasticity, Roughness, and Density: Results of a Randomized, Placebo-Controlled, Blind Study.(opens in a new tab)
Randomised controlled trial · Nutrients · 2019 · PMID 31627309
Effect of biotin supplementation in infant formula: A multi-center study in Japan.(opens in a new tab)
Clinical trial · Pediatrics international : official journal of the Japan Pediatric Society · 2023 · PMID 36680523
Efficacy of intramuscular injections of biotin and dexpanthenol in the treatment of diffuse hair loss: A randomized, double-blind controlled study comparing two brands.(opens in a new tab)
Randomised controlled trial · Dermatologic therapy · 2022 · PMID 35791704

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

Interaction
Interferes with blood tests, including the heart attack assay
Interacts withTroponin, thyroid function, hormone and vitamin D immunoassays
High-dose biotin distorts immunoassays that use biotin-streptavidin binding, which covers many common tests. It can produce falsely low troponin — risking a missed myocardial infarction — and falsely abnormal thyroid results that mimic Graves disease and have led to unnecessary treatment. The FDA has issued repeated warnings. Anyone taking high-dose biotin should tell the clinician ordering their blood tests, every time.
Worth knowing
Hair loss usually has another cause
Iron deficiency, thyroid disease, androgenetic alopecia, telogen effluvium after illness, and protein or energy restriction all cause hair loss far more often than biotin shortfall. Taking biotin instead of investigating those is the practical risk.
Worth knowing
Groups where deficiency is genuinely possible
Long-term carbamazepine, phenytoin or phenobarbital use, biotinidase deficiency, prolonged parenteral nutrition without supplementation, and regular consumption of raw egg white can all deplete biotin. These are the situations where a supplement corrects something.
Worth knowing
Gummy formats carry other ingredients
Many high-dose biotin products are gummies containing sugar and, in some cases, additional vitamins at doses that add up when combined with a multivitamin.

Biotin (vitamin B7)

What biotin (vitamin b7) may help with

About Biotin (vitamin B7)

What the research used

When it was taken

Any time

The evidence in depth

Blood glucose response

Hair growth and strength

Skin structure and hydration

Things to know

Interferes with blood tests, including the heart attack assay

Hair loss usually has another cause

Groups where deficiency is genuinely possible

Gummy formats carry other ingredients

What biotin (vitamin b7) may help with

About Biotin (vitamin B7)

What the research used

When it was taken

🕐Any time

The evidence in depth

Blood glucose response

Hair growth and strength

Skin structure and hydration

Things to know

Interferes with blood tests, including the heart attack assay

Hair loss usually has another cause

Groups where deficiency is genuinely possible

Gummy formats carry other ingredients

In the food catalogue

Any time