Biotin (high-dose)

Tier 3 — weak evidence · Hair · Nails · Skin

Biotin deficiency is rare in people who eat a normal diet. No trial evidence that supplements improve hair or nails in people who aren't deficient. Warning: doses above 5,000 mcg per day cause false results on heart and thyroid blood tests, which can lead to misdiagnosis. Stop high-dose biotin at least 48 hours before any lab work.

Dose: 30–100 mcg/day adequate; high-dose supplements (5,000–10,000 mcg) lack evidence and interfere with lab tests