phenytoin and St John's wort

Last reviewed 01/2018

St John's wort interacts with some anticonvulsants (carbamazepine, phenobarbitone, phenytoin) and leads to reduced blood levels of the anticonvulsant with consequent risk of seizures.

Suggested management of patients already taking SJW preparations:

  • check anticonvulsant levels and stop SJW
  • note that anticonvulsant levels may increase on stopping SJW
  • it may be necessary to adjust the dose of the anticonvulsant


  • CEM/CMO/2000/4