Biotin
Also known as vitamin B7, hair skin and nails supplements
The most heavily marketed hair supplement, and one of the least justified. Included here specifically so you can stop buying it.
$5–30/month — better spent elsewhere.
How it works
Biotin is a cofactor for carboxylase enzymes involved in keratin production. True biotin deficiency does cause hair loss and brittle nails — but it is genuinely rare, essentially confined to specific genetic disorders, prolonged parenteral nutrition, long-term anticonvulsant use or extreme raw egg white consumption. In people who are not deficient, supplementation produces no demonstrated benefit.
How it's used
Skip it unless a clinician has diagnosed a deficiency. If you have unexplained hair shedding, test ferritin, vitamin D, zinc and thyroid function instead — those find real, correctable causes. Importantly, stop biotin at least 72 hours before any blood test.
Trade-offs
In favour
- Harmless in itself
- Genuinely effective in the rare case of true deficiency
Against
- No evidence of benefit in people who are not deficient
- Diverts money and attention from interventions that work
- Ubiquitous in "hair, skin and nails" products at pointless megadoses
Risks and side effects
- Seriously interferes with immunoassay laboratory tests — including troponin, thyroid function and hormone panels. This has caused missed heart attacks and incorrect thyroid diagnoses. Stop biotin 72 hours before blood work and tell your doctor you take it.
How good is the evidence?
No credible evidence supports biotin supplementation for hair growth in people without deficiency. The laboratory interference risk is well documented and clinically significant.
Sources
- Biotin interference with laboratory tests — safety communicationUS FDA
- Biotin for hair and nail growth — evidence reviewPubMed
Sources point to guideline bodies and literature searches rather than single papers, so they stay accurate as the evidence moves.