Valerian (Valeriana officinalis) is a member of the Valerianaceae family of plants.  Valerian grows up to 30 - 150 cm tall. It has a single stem that ends in a terminal cyme of white, or pink flowers, which bloom June through September. The rhizome is ovoid-cylindrical and bears multiple roots which appear light to medium grey-brown, measuring 1-3 mm thick, and covered with coarse longitudinal furrows.  The leaves are pinnate. The root is the part of the plant used medicinally.
Valerian is native to Europe and Asia, and has been naturalized in North America. It grows wild in woodlands, along river banks, and in damp meadows. 
The primary constituents of interest in valerian are the valepotriates [valeriana-epoxy-triacylates, iridoid monoterpenes, isovaltrate, isovaleroxyhydroxy didrovaltrate (IVDH-valtrate), didrovaltrate, and acevaltrate]. Valerian also contains volatile oils accounting for 0.2 - 1.0% of it chemical content. These chief components include; bornyl isovalerenate and isovalerenic acid (both aroma-carriers), (-)-bornyl acetate, and isoeugenyl valerenate and isoeugenyl isovalerenate. In some strains valerenal, valeranone, cryptofaurinol also contribute to the volatile oil content.
Sesquiterpenes are contained in this plant as well, including valerenic acid (0.1 -0.9%), 2-hydroxyvalerenic acid and 2-acetoxy-valerenic acid. Other constituents in valerian include pyridine alkaloids (actinidine, valerianine, alpha-methylpyrrylketone) and caffeic acid derivatives like chlorogenic acid. 
Valerian in combination with hops is capable of reducing and/or inhibiting (depending on dose) the arousal induced by caffeine.  In a study of 32 volunteers, a valerian preparation 60 minutes after oral administration, was bioavailable and acted as a partial agonist to caffeine. The valerian/hop extract acted via a central adenosine mechanism which the authors conclude is possibly the reason for its sleep-inducing and sleep-maintaining activity. Valerian has also shown the ability to partially inhibit ascorbate/iron-induced peroxidation in rats; which may be important in treating neurodegenerative disorders. 
Medicinal actions ascribed to valerian include;
- sedative (paradoxical stimulant)
Traditionally, valerian was used as a cerebral stimulant for hysteria, chorea, hemicrania, all with mental depression and despondency; for cerebral anemia and mild spasmodic movements.  It was also used for gastrointestinal disorders, gynecological conditions, and other inflammatory problems.
Most of the research conducted on valerian has focused on the sedative or hypnotic effect of the root. A number of studies have been conducted over the years, some conflicting. However, it appears that the majority of research supports the use of valerian for sleep problems. An initial experiment involved 128 subjects who were given 9 samples to test: 3 containing placebo, 3 containing 400 milligrams of valerian extract, and 3 containing a proprietary over-the-counter valerian preparation.  The results showed that valerian produced a significant decrease in subjectively evaluated sleep latency scores and a significant improvement in sleep quality. Quality of sleep was improved more so among people who considered themselves poor or irregular sleepers, smokers, and people who thought they normally had long sleep latencies.
Another early double-blind test showed 44% percent of subjects experienced perfect sleep and 89% reported improved sleep from a valerian preparation versus placebo; as well, no side effects were observed.  The conclusion of a randomized, double-blind, placebo-controlled, cross-over study was that treatment with an extract of valerian root demonstrated positive effects on sleep structure and sleep perception of insomnia patients, and can therefore be recommended for the treatment of patients with mild psychophysiological insomnia.  In comparison to the pharmaceutical, oxazepam (10mg/day), over a 6 week treatment phase, a valerian extract (600 mg/day) showed a comparable efficacy in treating non-organic insomnia. 
As mentioned, conflicting studies also exist. The most recent includes a double-blind, placebo-controlled study published in late 2004. A three way crossover clinical trial was completed using 16 sleep-disturbed subjects averaging 56 years in age.  Following a 9pm dose of valerian 300mg, valerian 600mg, or placebo, patients were observed by EEG in a laboratory setting. In the morning a psychometric evaluation was conducted. The results showed no significant effect between valerian 300mg, valerian 600mg, or placebo on any EEG parameter or psychometric measure. The authors concluded that at this dosage level, valerian is ineffective for acute sleep problems.
Another trial of patients with chronic insomnia demonstrated no significant difference between valerian and placebo in promoting sleep or sleep related factors.  Nevertheless, a review published in American Family Physician concluded that valerian improves subjective experiences of sleep when taken nightly over one- to two-week periods.  Furthermore, they stated that it appears to be a safe sedative/hypnotic choice in patients with mild to moderate insomnia. The conflicting negative studies mostly involve single doses of valerian, whereas those experiments employing longer treatment periods usually result in positive effects in subjects with moderate insomnia.
In healthy subjects, valerian appears to have no measurable effects, making it a favorable choice over prescription medications like benzodiazepines due to the lack of detrimental side effects. Various doses of a valerian extract (600, 1200, and 1800mg) and 10 mg diazepam (positive control) were compared to placebo in 10 young healthy volunteers.  No significant effects were noted upon administration of valerian extracts, suggesting that acute administration of valerian does not have mood-altering or psychomotor/cognitive effects in young healthy volunteers. Other trials using valerian extract (500mg and 1000mg, or 400mg and 800mg dosages) also showed that cognitive or psychomotor performance were unaffected in healthy volunteers. [15, 16]
Valerian may also be of benefit in the treatment of stress and anxiety disorders. A pilot study was conducted of patients with stress-induced insomnia who were treated for 6 weeks with 120mg of kava daily, followed by 2 weeks off. Participants were then given 600mg of valerian daily for an additional 6 weeks.  The results showed that insomnia was not only improved, but total stress severity was significantly relieved by both compounds. Another experiment showed that valerian may be beneficial to health status by reducing physiological reactivity during stressful situations as evidenced by measurements of blood pressure and heart rate during laboratory- induced mental stress.  A randomized double-blind, placebo-controlled trial concluded that valepotriates (at a mean dose of 81.3 mg) may have a potential anxiolytic effect on the psychic symptoms of generalized anxiety. 
In addition, valerian may help with withdrawal symptoms from benzodiazepine use and for treating depression in comorbidity with anxiety disorders, when taken in combination with St. Johns Wort. [20, 21]
Dosages are dependent on the type of preparation and the intended condition to be treated. Most studies use a dosage range between 300 - 600mg of valerian root extract for treatment of insomnia. Valerian should be taken within 30 minutes to two hours before intended bedtime. 
Consumption of alcohol should be avoided when taking valerian. Likewise, valerian should not be taken with certain medications, as it may potentiate the sedative effects of barbiturates, anesthetics, and other central nervous system depressants. No contraindications for particular disease states and conditions have been reported.
When taken as recommended, valerian appears to be a safe herb. Valerian preparations given in single or repeated evening administrations at a dosage level of 600mg do not have a relevant negative impact on reaction time, alertness, and/or concentration the morning after intake.  The most commonly noted side effect in one study was the appearance of vivid dreams.  Other side effects that have been also rarely reported are gastrointestinal upset and migraine headaches. 
1. Tilgner S. Herbal Medicine from the Heart of the Earth. Wise Acres Press, Inc. Creswell, OR, 1999:111.
2. Botanical Medicine Class Notes. Bastyr University, Kenmore, WA. 2002.
3. PDR for Herbal Medicines. Medical Economics Company Inc., Montvale, NJ. 2001
4. Schellenberg R et al. The fixed combination of valerian and hops (Ze91019) acts via a central adenosine mechanism. Planta Med. 2004;70(7):594-7.
5. Malva JO, Santos S, Macedo T. Neuroprotective properties of Valeriana officinalis extracts. Neurotox Res. 2004;6(2):131-40.
6. Felter, H. W., Lloyd, J.U. King’s American Dispensatory, 18th ed.. Eclectic Medical Publications. Sandy, OR. 1898
7. Leathwood PD et al. Aqueous extract of valerian root (Valeriana officinalis L.) improves sleep quality in man. Pharmacol Biochem Behav. 1982;17(1):65-71.
8. Lindahl O, Lindwall L. Double blind study of a valerian preparation. Pharmacol Biochem Behav. 1989;32(4):1065-6.
9. Donath F et al. Critical evaluation of the effect of valerian extract on sleep structure and sleep quality. Pharmacopsychiatry. 2000;33(2):47-53.
10. Ziegler G et al. Efficacy and tolerability of valerian extract LI 156 compared with oxazepam in the treatment of non-organic insomnia–a randomized, double-blind, comparative clinical study. Eur J Med Res. 2002;7(11):480-6.
11. Diaper A, Hindmarch I.A double-blind, placebo-controlled investigation of the effects of two doses of a valerian preparation on the sleep, cognitive and psychomotor function of sleep-disturbed older adults. Phytother Res. 2004;18(10):831-6.
12. Coxeter PD et al. Valerian does not appear to reduce symptoms for patients with chronic insomnia in general practice using a series of randomised n-of-1 trials. Complement Ther Med. 2003;11(4):215-22.
13. Hadley S, Petry JJ. Valerian. Am Fam Physician. 2003 Apr 15;67(8):1755-8.
14. Gutierrez S et al. Assessing subjective and psychomotor effects of the herbal medication valerian in healthy volunteers. Pharmacol Biochem Behav. 2004;78(1):57-64.
15. Hallam KT et al. Comparative cognitive and psychomotor effects of single doses of Valeriana officianalis and triazolam in healthy volunteers. Hum Psychopharmacol. 2003;18(8):619-25.
16. Glass JR et al. Acute pharmacological effects of temazepam, diphenhydramine, and valerian in healthy elderly subjects. J Clin Psychopharmacol. 2003;23(3):260-8.
17. Wheatley D. Kava and valerian in the treatment of stress-induced insomnia. Phytother Res. 2001;15(6):549-51.
18. Cropley M et al. Effect of kava and valerian on human physiological and psychological responses to mental stress assessed under laboratory conditions. Phytother Res. 2002;16(1):23-7.
19. Andreatini R et al. Effect of valepotriates (valerian extract) in generalized anxiety disorder: a randomized placebo-controlled pilot study. Phytother Res. 2002;16(7):650-4.
20. Poyares DR et al. Can valerian improve the sleep of insomniacs after benzodiazepine withdrawal? Prog Neuropsychopharmacol Biol Psychiatry. 2002;26(3):539-45.
21. Muller D, Pfeil T, von den Driesch V. Treating depression comorbid with anxiety–results of an open, practice-oriented study with St John’s wort WS 5572 and valerian extract in high doses. Phytomedicine. 2003;10 Suppl 4:25-30.
22. Kuhlmann J et al. The influence of valerian treatment on “reaction time, alertness and concentration” in volunteers. Pharmacopsychiatry. 1999;32(6):235-41.