How does valerian work?

Many chemical constituents of valerian have been identified, but it is not known which may be responsible for its sleep-promoting effects in animals and in in vitro studies. It is likely that there is no single active compound and that valerian's effects result from multiple constituents acting independently or synergistically.

Two categories of constituents have been proposed as the major source of valerian's sedative effects. The first category comprises the major constituents of its volatile oil including valerenic acid and its derivatives, which have demonstrated sedative properties in animal studies. However, valerian extracts with very little of these components also have sedative properties, making it probable that other components are responsible for these effects or that multiple constituents contribute to them. The second category comprises the iridoids, which include the valepotriates. Valepotriates and their derivatives are active as sedatives in vivo but are unstable and break down during storage or in an aqueous environment, making their activity difficult to assess.

A possible mechanism by which a valerian extract may cause sedation is by increasing the amount of gamma aminobutyric acid (GABA, an inhibitory neurotransmitter) available in the synaptic cleft. Results from an in vitro study using synaptosomes suggest that a valerian extract may cause GABA to be released from brain nerve endings and then block GABA from being taken back into nerve cells. In addition, valerenic acid inhibits an enzyme that destroys GABA. Valerian extracts contain GABA in quantities sufficient to cause a sedative effect, but whether GABA can cross the blood-brain barrier to contribute to valerian's sedative effects is not known. Glutamine is present in aqueous but not in alcohol extracts and may cross the blood-brain barrier and be converted to GABA. Levels of these constituents vary significantly among plants depending on when the plants are harvested, resulting in marked variability in the amounts found in valerian preparations.

What is the regulatory status of valerian in the United States?

In the United States, valerian is sold as a dietary supplement, and dietary supplements are regulated as foods, not drugs. Therefore, premarket evaluation and approval by the Food and Drug Administration are not required unless claims are made for specific disease prevention or treatment. Because dietary supplements are not always tested for manufacturing consistency, the composition may vary considerably between manufacturing lots.

Can valerian be harmful?

Few adverse events attributable to valerian have been reported for clinical study participants. Headaches, dizziness, pruritus, and gastrointestinal disturbances are the most common effects reported in clinical trials but similar effects were also reported for the placebo. In one study an increase in sleepiness was noted the morning after 900 mg of valerian was taken. Investigators from another study concluded that 600 mg of valerian (LI 156) did not have a clinically significant effect on reaction time, alertness, and concentration the morning after ingestion. Several case reports described adverse effects, but in one case where suicide was attempted with a massive overdose it is not possible to clearly attribute the symptoms to valerian.