The research is not yet good enough to confirm those claims, but the risk is minimal.
Mental Health Implications
Research suggests that valerian may be helpful for sleep disorders, but there is not enough evidence from well-designed studies to confirm this. Three of the eight sources discussing valerian decline to recommend its use for sleep disorders, citing inadequate evidence, despite its traditional use in the United States, Europe and Japan. Brown et al II's 2013 statement would raise the dissent to 50% -- 4 of 8. In the sleep laboratory, the effects of valerian were not significantly different from those of placebo, and a 2007 meta-analysis concluded that no rigorous studies had found any significant effect of valerian on sleep.
There is not enough scientific evidence to determine whether valerian works for anxiety (the sources are split 3 to 3 on the use of valerian for anxiety) or for other conditions, such as headaches, depression, menopausal symptoms, sedation, irregular heartbeat and trembling.
Despite the lack of persuasive clinical evidence of efficacy in treating insomnia, sleep quality remains to be studied, and subjective reports still hold out hope. Valerian may not be ideal for acute treatment of insomnia, but some evidence and analysis suggests that it may be effective in the promotion of natural sleep after several weeks of use. Since it appears relatively safe as long as drug interactions are avoided, valerian may be a CAM support to help with sleep even if it can't cure chronic insomnia.
The Natural Standard cautions that valerian may increase the amount of drowsiness brought on by other drugs or herbs. Berkeley Wellness specifically counsels that valerian not be taken with alcohol, tranquilizers or barbiturates. Valerian interacts with anesthetics and so must be discontinued before surgery.
Valerian can cause mild side effects, such as occasional gastrointestinal effects, headaches, dizziness, excitability, uneasiness, unsteadiness, low body temperature, tiredness the morning after its use, and a "hangover" from large doses. Similarly, "valerian withdrawal" may occur if the consumer stops using the drug suddenly after long-term high-dose use. This may entail confusion and rapid heartbeat. Valerian is classified by the FDA as "generally regarded as safe," and some researchers refer to valerian as "quite safe." Long-term use may result in insomnia. Slight reductions in concentration and ability to perform complicated thinking may occur for few hours after taking valerian. Use caution if driving or operating heavy machinery.
Brown et al. caution against use of valerian in pregnancy or in association with hepatic disease. Safety for children has been more studied but is still controversial. Accordingly, it cannot be recommended. In the absence of a standard extract, no recommendation can be made on dosage.
Promising, but not yet proven. The split of the sources confirms that this is a controversial supplement, even though it appears benign (except for the odor and taste).
For detailed information on Valerian and other treatments, download the full review.