Topical niacin may be an effective thinning hair treatment for women. A special form of niacin is required—one that is lipophilic (myristyl nicotinate) and can penetrate deeply into the skin (this type is often used to treat photodamaged skin).

This treatment requires a prescription. Large doses of oral niacin can have serious side effects and will not improve hair growth unless one is niacin-deficient. Oral niacin supplements should not be applied to the skin.