Conflict of Interests - none
The NLH Q&A Service has answered this question. The most meaningful quote being: "There are no reports in the scientific literature to suggest that valerian interacts with any conventional medications. However, valerian is a sedative herb that may increase the effects of alcohol and medications for anxiety and insomnia. Valerian should not be combined with barbiturates (medications, such as pentobarbital, prescribed for sleep disorders or seizures), and should be used with caution, if at all, by people taking benzodiazepines (anti-anxiety and sleep inducing medications including alprazolam, diazepam, and lorazepam) or other sedative medications (such as antihistamines)." Source: http://www.clinicalanswers.nhs.uk/index.cfm?question=5202