There is a lack of scientific evidence of the safety and efficacy of herbal medicines together with an under-reporting and underestimation of adverse effects. Interactions between herbal medicines and conventional medicines are poorly studied and may be unpredictable.
The clinical importance of any interaction depends on a variety of factors, such as other co-administered medicines, the health status of the patient, the composition of the herbal medicine and the dosage regimens used. A lack of a documented interaction with a medicine does not mean that an interaction does not exist; it may not yet have been reported.
Currently, four non-VKA [vitamin K antagonist] oral anticoagulant (NOAC) drugs are available on the UK market as alternatives to warfarin: dabigatran, rivaroxaban, apixaban and edoxaban.
This Q&A considers the pharmacokinetic and pharmacodynamic interactions between NOACs and some herbal medicines including black cohosh, dong quai, echinacea, evening primrose oil, garlic, ginkgo, Panax ginseng, Siberian ginseng, saw palmetto and St. John’s wort.