Biotin is one of the B vitamins, sometimes called vitamin B7 or vitamin H. It is sometimes taken as a supplement as it is thought to improve health of hair, skin and nails. It is also being increasingly used in the treatment of Multiple Sclerosis.

Unfortunately taking high doses of Biotin (more than 5mg a day) can result in falsely abnormal tests of Thyroid Function. This is because the Biotin can interfere with some (but not all) laboratory tests for thyroid function. In a worse case scenario this could lead to inappropriate and potential harmful treatment for thyroid disease if the doctors involved do not know their patient is taking Biotin.

Doses of Biotin commonly found in multivitamins are not high enough to cause this problem (typically 30 – 50 micrograms – 0.03 – 0.05 mg). However, some people take high doses for hair and nail health; more than 5mg a day and patients with Multiple Sclerosis are sometimes treated with up to 300mg per day. It is important that these patients notify their doctors of this to enable them to interpret unusual blood tests, particularly thyroid hormone, and if necessary re-test at a different laboratory.

In fact it is good practice to let all you health practitioners know about all supplements that you take as many of these may interfere with other medications/treatments.