Health Reference LibraryHow much biotin should I take, and can you take too much?
This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.
Summary
For general health, none: a normal diet supplies about 40 micrograms a day against a safe and adequate intake of 10 to 200 micrograms, and there is no UK reference intake because deficiency is rare. The high doses sold for hair and nails, 2500 to 10000 micrograms a day, rest on small studies in people with brittle nails, and there is no good trial showing hair growth in people who are not short of it. The NHS says 900 micrograms a day is unlikely to cause harm, and no toxic dose has been found, but high dose biotin distorts many blood tests, including thyroid, so stop it two days before any test and tell whoever takes the sample.
Dose calculator: capsules to reach your biotin target
Enter the daily amount of biotin you are aiming for and see how many servings of each Nutri Tailor product reach it. Nothing you enter leaves this device. No AI is used.
This tool does arithmetic on the label figures. It is not personal dosing advice and it knows nothing about your history or blood results. The reference intake, the safe upper guide and the trial doses are on this page; talk to your GP or a registered nutritional therapist before changing what you take.
Effective dose
The reference intake is no UK reference intake; a safe and adequate intake is 10 to 200 micrograms a day, and a normal diet supplies about 40. For general nutrition, food is enough and a supplement is unnecessary. The high doses sold for hair and nails, 2500 to 10000 micrograms a day, come from small studies in people with brittle nails and from case reports in true biotin deficiency, which is rare; there is no good trial showing hair growth in people who are not deficient. If you try a high dose, give it three to six months, because nails grow slowly, and stop if nothing changes.
Safety profile
How much is too much: the NHS says 0.9 mg (900 micrograms) or less a day from supplements is unlikely to cause harm. Biotin is water soluble and no toxic dose has been found; the NHS guide of 900 micrograms is a caution, not a toxicity line. The one real problem with high doses is that biotin interferes with many blood tests, including thyroid and troponin assays, giving false results. Stop biotin at least two days before any blood test and tell whoever takes the sample.
Guideline positions
NHS vitamins and minerals guidance for biotin. NIH Office of Dietary Supplements fact sheet for biotin where one exists. The trial doses quoted above are from the sources listed on this page.
Practical framework
Capsules to reach the dose, from the Nutri Tailor range, all made in the UK: [biotin capsules](/products/biotin), 8000 micrograms (8 mg) per capsule, the hair and nail dose; well above the NHS guide, so plan a defined course rather than indefinite use. To read your own result against the UK ranges, use the free blood test result interpreter. This is a summary of published research, not personal health advice. Talk to your GP or a registered nutritional therapist before changing what you take, especially if you are pregnant, have a diagnosed condition or are under ongoing care.
Common misconceptions
That more biotin works faster: above the doses the trials used there is no extra effect, only more side effects. That the front of the bottle states the dose: read the per capsule figure and the serving size on the back. That the NHS figure is a toxic threshold: it is the level below which harm is unlikely, which is a different thing.
Sources
- 2025. Biotin Fact Sheet for Health Professionals. NIH Office of Dietary Supplements.
- 2024. B vitamins and folic acid. NHS.
- Testing.com 2020. New Guideline Addresses Biotin Interference in Some Lab Tests. Testing.com.