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St John's wort - Hypericum perforatum

This information explains what St John's wort is used for, how it works, possible side effects and interactions with other medicines.

Can I take St John's wort with other medication?

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.

Why might I need advice if I'm taking other medication?

If you are considering taking or are already taking St John's wort at the same time as any other prescription or over-the-counter medications, it is really important to get professional advice from a pharmacist or your doctor.

They will be able to talk to you about any possible interactions St John's wort may have with your medications and discuss alternative treatments or dosages.

These are some of the common drug interactions with St John's wort:

  • Antidepressants – you should not take St John's wort at the same time as any other antidepressant. Combining the two medications can make your depression worse and can lead to serotonin syndrome.
  • Sleeping pills and anaesthetics – St John's wort may prolong the effects of some sleeping pills and anaesthetics. If you are taking St John's wort and are to receive a general or local anaesthetic, you should inform the anaesthetist.
  • Contraceptives (including emergency contraception) – St John's wort can reduce the level of contraceptives in the blood and make them less effective, increasing the risk of pregnancy and breakthrough bleeding.

Other medications identified as interacting with St John's wort include:

  • antipsychotics 
  • anticoagulants, to thin the blood
  • immunosuppressants, to prevent the body from rejecting a transplanted organ.

It can also reduce the effectiveness of common medications to treat:

  • cholesterol
  • heart disease
  • high blood pressure
  • migraines
  • epilepsy
  • cancer
  • hepatitis C
  • HIV and AIDS.

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.

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