St John's wort (Hypericum perforatum) modestly increased the clearance of single-dose
carbamazepine, but had no effect on multiple-dose
carbamazepine in one study.
Before the publication of these studies the CSM in the UK had advised that patients taking
carbamazepine should not take St John's wort. This advice was based on predicted pharmacokinetic interactions. In the light of the above studies, this advice may no longer apply.