Valerian is not considered toxic or dangerous at recommended dosage. There is also no evidence of unfavorable outcomes if used during pregnancy.
However, if you are considering using Valerian and have a pre-existing condition, or are pregnant, then seek the advice of a medical professional first.
Due to the sedative effects of Valerian, vehicles and heavy machinery should not be operated when under its influence.
It is rare, but for some the sedating compounds of Valerian actually act as a stimulant, so a small dose should be taken on the first use to see how the body reacts to it.
There have been instances where stomach irritation, headaches and other minor adverse effects have been reported. However, no clinical trial has ever found solid evidence of such side effects, and they are often resulting from other factors. This would indicate that Valerian could potentially interact with other medication adversely, however, this is also something that has yet to be proven, with no clinical trials finding any significant interactions.