From American Academy of Family Pediatrics
Valerian is a safe herbal choice for the treatment of mild insomnia and has good tolerability. Most studies suggest that it is more effective when used continuously rather than as an acute sleep aid; more rigorous studies are needed to confirm these results. A potential advantage of valerian over benzodiazepines is the lack of sleepiness on awakening when used at the recommended dosages. Valerian also may be helpful in weaning patients with insomnia from benzodiazepines. The use of valerian as an anxiolytic requires further study. Long-term safety studies are lacking.
Dosage
Based on the reviewed studies, the effective dosage of valerian root extract for treatment of insomnia ranges from 300 to 600 mg. An equivalent dose of dried herbal valerian root is 2 to 3 g, soaked in one cup of hot water for 10 to 15 minutes.25 The product should be ingested 30 minutes to two hours before bedtime.
from wikipedia
Oral forms
Oral forms are available in both standardized and unstandardized forms. Standardized products may be preferable considering the wide variation of the chemicals in the dried root, as noted above. When standardized it is done so as a percentage of valerenic acid or valeric acid. Physician Formulas makes a 300 mg capsule standardized to 0.8% valerenic acid (2.4mg). Nature’s Sunshine Time-Release Valerian tablet contains 500 mg of valerian root extract standardized to 0.8% valerenic acid (4mg). Nature Made makes a 400mg capsule standardized to only 0.07% valerenic acid (0.28mg). Nutraceutical makes two 50mg capsules under the names Solaray and Thompson standardized to 0.8% valeric acid (0.4mg).Dosage is difficult to determine due to the lack of standardization and variability in available forms. Typical dosages of the crude herb vary from 1-10 grams per day. Valerian root is non-toxic but may cause side effects in excessive doses.