**Biotin** at 5,000 mcg puts you at the top of the typical supplement range, well above the 30 mcg RDA. The catch: clinical research supporting biotin for hair and nail growth is largely limited to people with actual biotin deficiency or brittle nail syndrome. If you're not deficient, the evidence that this dose will improve your hair is thin.

At 5,000 mcg you're getting a meaningful dose for metabolic support — biotin is a cofactor your body uses to process fats, carbohydrates, and amino acids. The single-capsule serving keeps things simple, and 120 capsules give you a four-month supply.

One important caveat: biotin at this dose can interfere with blood tests, including thyroid panels and cardiac markers. If you have lab work coming up, stop taking it at least 48 hours beforehand — this is something most labels mention but few people actually notice.