Biotin (vitamin B7)

Sold for hair, skin and nails. There is no trial showing it helps them unless you are short of it, and doses of 1 mg or more can make blood tests come out wrong.

At a glance

Our verdict	No evidence it helps hair or nails without a deficiency, and high doses make blood tests wrong, including the heart test used for chest pain.
Sold for	Hair, skin and nails (claimed)
How sure the evidence is	No evidence (no trial) for hair and nails; High that it upsets blood tests
Cost a month	About $5 to $10 (estimated)

Written for adults in Canada. It explains the evidence; it is not advice for you personally. Last reviewed 20 October 2026.

Supplement Check

Is it right for you?

Taking a hair, skin and nail product? It may contain enough biotin to upset your blood tests. Your check finds it and tells you when to stop it. Our Supplement Check looks at:

Anyone with a blood test booked
Anyone being assessed for chest pain or a heart problem
Anyone having thyroid tests, or taking levothyroxine while the dose is adjusted
Anyone having a pregnancy blood test
Every medicine you take
The total across everything you already take, against the safe upper limits

Coming soon. The Supplement Check and the Online Health Assessment open once our safety testing is complete.

$59 when it opens, paid once. Adults 18 and over, anywhere in Canada. While the service is new, Dr. French reads every report himself, and your report arrives within 3 working days. More about the Supplement Check

Tell me when it opens

What it is

A water-soluble B vitamin that helps enzymes (carboxylases) in the body's energy reactions. Adults need about 30 µg a day; a multivitamin gives about that, which does not affect blood tests. [1, 2] Health Canada caps biotin in a multivitamin at 500 µg, but single-ingredient biotin products are licensed up to 20 mg a day. [3, 4] It is sold mostly in hair, skin and nail products, and in some B-complex products. Very high doses (100 to 300 mg) have been trialled in progressive multiple sclerosis.

Structure of Biotin (vitamin B7) — Structure: PubChem (public domain).

How it acts

In the body it is a helper (coenzyme) for energy reactions; extra does nothing more for hair or nails unless you are short of it.

The problem is in the laboratory. Many blood tests use biotin as a chemical “hook” to catch what they measure. Extra biotin in your blood takes up the hooks, so some tests read falsely low (troponin, the heart test for chest pain; thyroid-stimulating hormone (TSH); parathyroid hormone; the heart-failure test NT-proBNP; prostate-specific antigen (PSA); ferritin; the pregnancy hormone hCG) and others falsely high (thyroid hormones free T4 and T3, vitamin D, cortisol). [5, 6] The result can look exactly like an overactive thyroid (Graves' disease) when the thyroid is normal. [7]

Outline of a person showing where Biotin (vitamin B7) acts in the body

What it is used for, and what the evidence says

Use	What the trials found	How sure we are
Hair, skin and nails without a deficiency	We found no trial showing any benefit.	No evidence (no trial)
Blood test errors (harm)	In healthy adults, 10 mg a day for 7 days distorted 9 of 23 common blood tests. [5]	High
The heart test for chest pain (harm)	The US Food and Drug Administration reported falsely low troponin results from biotin, and one death. Supplements of 20 mg are common, some give 100 mg a pill, and 300 mg a day produced blood levels up to 1,200 ng/mL. [6] Some troponin tests have been reformulated to tolerate biotin (one maker's new lots tolerate 1,200 ng/mL), [8] but not all. [6]	High
Thyroid tests (harm)	The European Thyroid Association's 2026 guideline says biotin and other test interference must be ruled out before diagnosing rare thyroid conditions. [9]	Guideline
How long to stop before a blood test	No study has measured it. The FDA says it is not known whether stopping for any number of hours prevents wrong results. [6] Alberta's laboratories advise 48 hours for doses over 1 mg. [2] We advise at least 3 days, because no safe interval is proven.	Moderate

How sure we are: High means further research is very unlikely to change the answer; Moderate, it might; Low, it may well change; Very low, we are very unsure. These follow the GRADE method that guideline panels use.

Benefits

None shown for hair, skin or nails in people who are not short of biotin. There is no trial.

Risks and side effects

A heart attack can be missed. Biotin can make the troponin test read falsely low; the FDA has reported one death. [6]
Wrong thyroid results that look like an overactive thyroid, which can lead to the wrong diagnosis or the wrong thyroid dose. [7]
Other wrong results: parathyroid, heart-failure, prostate, iron-store, pregnancy, vitamin D and cortisol tests. [5]
Health Canada warned in January 2025; no serious Canadian case has been reported. [1]

Interactions with medicines

Biotin's main interaction is with laboratory tests, not with medicines. It does not speed up or block the liver enzymes (cytochrome P450) that clear medicines, and no medicine interaction was listed in our review.

Medicine	What can happen	What to do
Troponin (heart test for chest pain)	Falsely low; a heart attack can be missed	Tell the emergency team you take biotin
Thyroid tests (TSH, free T4, T3)	Falsely suggest an overactive thyroid	Stop at least 3 days before; tell the laboratory
Thyroid tests while your levothyroxine dose is being adjusted	Wrong results can lead to the wrong dose	Stop at least 3 days before each test
Parathyroid hormone, NT-proBNP, PSA, ferritin, hCG, vitamin D, cortisol	Falsely high or low	Stop at least 3 days before; tell the laboratory

Who should not take it

Anyone with a blood test booked.
Anyone being assessed for chest pain or a heart problem.
Anyone having thyroid tests, or taking levothyroxine while the dose is adjusted.
Anyone having a pregnancy blood test.
Under 18: outside the Supplement Check.

Dose and timing

We do not recommend a dose. There is no hair or nail trial to give a reference dose. Adults need about 30 µg a day, which a multivitamin supplies; high dose means over 1 mg.
If you take 1 mg a day or more: stop it at least 3 days before any blood test, and tell whoever takes your blood that you take it. If you go to hospital with chest pain, tell them.
Look on the label of hair, skin and nail products and B-complex products. 95% of Canadian licences at 1 mg or more carry a laboratory-test warning. [4]
There is nothing to measure to tell whether it is working.

What we know about Canadians

No Canadian survey measures biotin use. Of 717 licensed biotin, hair and nail products, 282 (39%) give 1 mg a day or more, 79 give 10 mg or more, and the highest is 20 mg; 95% of those at 1 mg or more carry the laboratory-test warning. [4] Health Canada has reported no serious Canadian case. [1]

How sure are we: very low. No data on how many Canadians take biotin; product counts are high certainty, from a scan of every active licence (20 Oct 2026).

An honest comparison: hair and nails

No medicine or lifestyle option for hair and nails was compared in our review.

Option	Effect	How sure we are	Cost a month (CAD)
Biotin	No evidence without a deficiency	Very low	$5 to $10 (estimated)
Enough protein; iron if low	Not compared in our review	Not graded	—
Assessment by a physician (iron, thyroid, treatment for pattern hair loss)	Not compared in our review	Not graded	—

Read honestly: hair loss has causes that can be found and treated, and biotin can hide one of them by upsetting the thyroid test.

Why we don't recommend it

We do not sell biotin and our check never recommends it. It has no proven benefit for hair, skin or nails, and at 1 mg a day or more it can make blood tests wrong.

Already taking it? You can stop it. If you keep it, stop it at least 3 days before any blood test and tell the laboratory; if you go to hospital with chest pain, tell them. If your hair is thinning, see your doctor: iron, thyroid and pattern hair loss can be checked and treated.

There is no trial of biotin for hair or nails in people who are not short of it, and almost nobody is. The harm is real and specific: a falsely low heart test can delay treatment of a heart attack, and wrong thyroid results can lead to wrong treatment. Because no study shows how long biotin must be stopped to be safe, our current advice is at least 3 days, longer than Alberta's laboratory rule of 48 hours. A product with no benefit and a known harm is not one we sell.