Critical evaluation of the effect of valerian extract on sleep structure and sleep quality 

This randomised double-blind placebo-controlled study published in 2000 investigated short- and long-term supplementation of valerian extract in sleep parameters. Sixteen participants diagnosed with insomnia (psychophysiological) were enrolled in this study. Objective polysomnographic (8 recordings) and subjective parameters of sleep quality were tested. Single doses of valerian had no immediate impact on sleep structure however, after multiple doses there was a statistically significant improvement in the valerian arm relating to reducing the latency of slow wave sleep induction. Subjects also demonstrated increase in REM percentage, low number of adverse effects, and increased “time in bed” measurements. 

References:

Donath F, Quispe S, Diefenbach K, Maurer A, Fietze I, Roots I. Critical evaluation of the effect of valerian extract on sleep structure and sleep quality. Pharmacopsychiatry. 2000;33(2):47-53. doi:10.1055/s-2000-7972