Valerenic acid, an ingredient of the root, acts on chemical pathways in the brain that control a person's level of anxiety or relaxation, according to scientific literature.

WSJ: Can a Root Get to the Problem of Insomnia?

Preparations of the herb, including the amount of valerenic acid, vary widely from study to study, making it hard to draw firm conclusions, says Catherine Ulbricht, co-founder of Natural Standard and a pharmacist at Massachusetts General Hospital in Boston.

WSJ: Can a Root Get to the Problem of Insomnia?