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This information explains what St John's wort is used for, how it works, possible side effects and interactions with other medicines.
St John's wort has significant interactions with a large number of medicines which are in common use.
This means that it may affect the way that the body processes other medications which may make them less effective, or increase the chances of adverse effects. These medications include both prescribed drugs and medicines that you can buy for yourself over the counter.
These are some of the common drug interactions with St John’s wort:
Other medications identified as interacting with St John's wort include:
It can also reduce the effectiveness of common medications to treat:
For a more detailed list of known medications that interact with St John's wort, you can visit the National Institute for Health and Care Excellence (NICE) website.
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.