More than 200 plant species belong to the genus Valeriana, but the one most commonly used as an herb is Valeriana officinalis. The root is used for medicinal purposes.

Galen recommended valerian for insomnia in the second century AD. From the sixteenth century onward, this herb became popular as a sedative in Europe (and later, the United States). Scientific studies on valerian in humans began in the 1970s, leading to its approval as a sleep aid by Germany's Commission E in 1985. However, the scientific evidence showing that valerian really works remains incomplete.

As with most herbs, we are not exactly sure which ingredients in valerian are most important.1,2Early research focused on a group of chemicals known as valepotriates, but they are no longer considered candidates. A constituent called valerenic acid has also undergone study, but its role is far from clear. Another substance in valerian, called linarin, has also attracted research interest.51

Our understanding of how valerian might function remains similarly incomplete. Several studies suggest that valerian affects GABA, a naturally occurring amino acid that appears to be related to the experience of anxiety.3-6Conventional tranquilizers in the Valium family are known to bind to GABA receptors in the brain, and valerian may work similarly. However, there are some significant flaws in these hypotheses, and the reality is that we don't really know how valerian works (or if, indeed, it really does).7,8

Valerian is commonly recommended as a mild treatment for occasional insomnia. However, evidence from the best positive study on valerian suggests that it is only useful when taken over an extended period of time for chronic sleep disorders.9Overall, it is not clear whether valerian is effective for sleep at all.64

Like other treatments used for insomnia, valerian has also been proposed as a treatment for anxiety, but there is no reliable evidence as yet that it is effective.

Finally, valerian is sometimes suggested as a treatment for a nervous stomach; however, as of yet, there is no supporting scientific evidence for this use.