Valerian is generally regarded as highly safe, with few side effects reported that are significantly different from those experienced with a placebo.
One meta-analysis noted a notable increase in the occurrence of diarrhea.[1]
Other side effects, such as nausea, epigastralgia (pain in the upper middle part of the abdomen), or heartburn, have been reported in some studies, but no significant difference was found between the intervention and the placebo group.[1]
Regarding adverse effects on the central nervous system, one study reported somnolence as a negative side effect when valerian was taken at night.[2] However, one meta-analysis found that while studies of valerian supplementation reported mild headache, nervousness, and drowsiness as side effects, these side effects weren’t significantly different from those experienced by participants who received a placebo.[1] Furthermore, valerian does not appear to impair cognitive or psychomotor functions in either healthy adults or the elderly, and no side effects were observed when valerian was taken for insomnia by either postmenopausal women or older women. Valerian also seemed to be safe when consumed by children between 7 and 14 years old with sleep problems and cognitive deficits, although this study only included 5 participants.[3]
Some of the studies included in one meta-analysis did report mild side effects, including vivid dreams, fatigue, dizziness, sleepiness, drowsiness, and depression. However, it was not possible to establish a causal relationship between the treatment with valerian and these adverse effects.[3]
Finally, valerian does not appear to interfere with the expression of enzymes of the cytochrome P450 (CYP) family, suggesting that the likelihood of a drug-supplement interaction with medications metabolized by this enzyme group is low.[3] Nonetheless, further research is required to explore potential interactions in more depth.