Many herbs interact with modern medicines in different ways and this can lead to serious problems in some instances. Because modern drugs are new, and interactions are complex, we still know very little about this potential health risk.

Take St John’s wort (Hypericum perforatum) as an example. One of the effects of St John’s wort is to enhance the function of a specific liver enzyme. By doing so St John’s wort accelerates the clearance of certain prescribed medicines that the liver metabolizes. This may lead to a reduced level of the prescribed medicine in the blood and so reduce its effectiveness as a treatment. Informing your veterinarian will allow for these herb-drug interactions to be taken into account. Your vet could then measure the drug levels in the blood and increase the dose if appropriate, or the St John’s wort could be discontinued for the treatment period.