This information explains what St John's wort is used for, how it works, possible side effects and interactions with other medicines.
Most St John’s wort products are licensed by the Medicines and Healthcare Products Regulatory Agency (MHRA). This organisation is responsible for licensing herbal medicines in the UK under the Traditional Herbal Medicines Registration (THR) scheme.
Under this scheme, registration is based on the long-standing use of a plant as a traditional herbal medicine, rather than being based on clinical trials.
Licensed St John’s wort products should be marked with the registration mark shown here.
This indicates that the herbal medicine is safe to an acceptable standard, provided it is used according to the instructions on the packaging. The product should also have a registration number, starting with the letters ‘THR’.
St John’s wort is available on prescription in many European countries. However, the use of St John’s wort is not currently recommended by the National Institute for Health and Care Excellence (NICE) so doctors in England and Wales do not normally write prescriptions for it.
This is because of uncertainty about appropriate doses, variations in preparations and the potentially dangerous interactions that it has with other commonly used medications. For more information, see our pages on dosage and interactions with medication.
Although doctors are advised not to prescribe St John's wort, you can buy it over the counter. It is readily available in pharmacies and in many health food shops.
This information was published in January 2020. We will revise it in 2023.
References are available on request. If you would like to reproduce any of this information, see our page on permissions and licensing.