St John’s wort and cancer

St John’s wort is a herbal remedy. It is used as a complementary therapy for mild depression and minor skin wounds.  


  • St John's wort is a plant with yellow flowers.
  • It is used for mild to moderate depression.
  • St John's wort can interact with certain cancer drugs and other medication.

What is St John's wort?

Other names for the herb St John's wort include hypericum, goatweed, klamath weed and tipton weed. The scientific name is Hypericum perforatum.

St John’s wort is a herbal remedy made from the flowers and unopened buds of the plant. It is a popular complementary therapy for mild to moderate depression. There is some scientific evidence to show that St John’s wort can help to reduce mild or moderate depression. But doctors have concerns about the possible side effects and the fact that it can interact with some cancer treatments.

Scientists believe that chemicals in the brain (neurotransmitters) play a part in causing depression. Two of the active ingredients in St John’s wort – hypericin and hyperforin – may change the activity of these neurotransmitters.

Why people with cancer use it

It is common for people with cancer to feel low or depressed. This could happen at any point during diagnosis, treatment or after treatment has finished.

Many people see St John’s wort as a non toxic and natural therapy that is safe to use. People with cancer may also use St John’s wort rather than talk to their doctor or nurse about feeling sad or depressed.

You can get St John's wort over the counter without a prescription. But you do need to be careful. Generally the side effects of St John’s wort are mild but it can interact with some other types of drugs so it is important to check with your doctor before taking it.

If you have symptoms of depression, it might be hard to talk to your doctor or specialist nurse. But they will be willing to listen and will want to help you through this difficult time. They can advise you about many ways of treating depression that don’t always involve taking drugs.

How you have it

St John’s wort comes as:

  • capsules
  • tablets
  • a powder
  • tinctures
  • a liquid extract
  • tea bags
  • creams to apply to the skin

You can buy various St John’s wort products in health food stores, chemists and over the internet. They may contain different amounts and types of extracts of St John’s wort.

In the UK and Europe it is important to buy only products that are registered under the Traditional Herbal Remedies (THR) scheme. Remedies that are registered under the scheme have a THR symbol on the packaging. THR products have been tested for quality and safety.

Side effects

Side effects are uncommon but St John's wort may cause:

  • headaches
  • constipation
  • stomach upsets
  • sleep disturbances
  • dizziness
  • tiredness
  • a dry mouth
  • skin rash
  • increased sensitivity to sunlight

Check with your doctor before using St John's wort if you are having radiotherapy. It can make your skin more sensitive. You should avoid going out in strong sunlight, and don’t use tanning beds or have skin laser treatment. There are a few reports of people developing a skin rash while taking St John’s wort.

We don’t know whether any of these side effects are long or short term. Side effects are usually mild. But as extracts of St. John's wort can change the effects of other drugs, you should talk to your doctor before using it.

Drugs that can interact with St John's wort

St John’s wort can change how well some drugs work, making them either stronger or weaker. We do not list all of the drug interactions here.

  • cancer drugs such as irinotecan, dasatinib, erlotinib, imatinib, sorafenib, sunitinib, etoposide and mitotane
  • cyclosporin and tacrolimus (drugs to prevent organ transplant rejection)
  • blood thinning drugs such as warfarin
  • some antibiotics
  • an asthma medicine called theophylline
  • heart medications such as digoxin
  • some epilepsy drugs
  • some HIV drugs
  • a pain killer called Oxycodone
  • different types of contraceptive medicine
  • some types of antidepressant medicine

You can have some serious side effects if you take St John's wort with these drugs. It is very important to talk to your doctor before taking this herbal supplement. 

Research into St John's wort

Several studies have looked at St John’s wort as a treatment for depression and compared it to other anti depressant drugs. This includes several large randomised clinical trials. Much of that research shows that certain extracts from St John’s wort can help treat mild to moderate depression.

These studies suggest that it is:

  • more effective than a dummy drug (a placebo)
  • as effective as standard anti depressant drugs

 A systematic review Open a glossary item in 2016 looked at St John's wort and depression. It said St John's wort can help with mild to moderate depression. They say we need more studies looking at severe depression. They also say there were limitations to the studies and not all the side effects were reported. 

Scientists are also looking at using St John’s wort for other mental health conditions such as anxiety, attention deficit hyperactivity disorder and obsessive compulsive disorder. There is also research into the safety of St John’s wort, and how it interacts with other drugs.

A few laboratory studies are testing some substances from St. John’s wort to see whether they could work as cancer treatments. But this is very early research and these substances have not yet been tested in humans.

Who shouldn’t use it

You shouldn’t take St John’s wort if you:

  • take other types of anti depressant medications
  • have manic depression (bipolar disorder)
  • are taking any drugs which will interact with it (check with your pharmacist or doctor)

You should not take St John’s wort if you are pregnant. It can increase womb contractions and may increase the risk of miscarriage. It can also pass into breast milk so should not be taken if you are breastfeeding.

You also need to stop taking St John’s wort at least 10 days before any surgery where you might need to have an anaesthetic.

How much it costs

The cost will vary depending on the dosage, the amount you buy and where you buy it. It can range from around £9 to £25 for 60 capsules.

A word of caution

Always tell your cancer doctor if you are planning on taking a herbal remedy such as St John's wort. If you are on other cancer drugs this is particularly important as St John's wort can interfere with some medication. 

  • Electronic Medicines Compendium - St John's wort 
    Accessed 2022

  • A systematic review of St. John's wort for major depressive disorder
    E. Apaydin and others
    Systematic Reviews, 2016. Volume 5, Issue 1

  • Herbal medicines in the treatment of psychiatric disorders: 10-year updated review.
    Phytotherapy Research July 2018.32(7):1147-1162. 

  • A critical approach to evaluating clinical efficacy, adverse events and drug interactions of herbal remedies.
    A.A Izzo and others
    Phytotherapy Research. February 2016

  • Complementary therapies for clinical depression: an overview of systematic reviews
    H Haller and others
    British Medical Journal, 2019. Volume 9, Issue 5

  • Antiproliferative Effects of St. John's Wort, Its Derivatives, and Other Hypericum Species in Hematologic Malignancies
    A Allegra and others
    International Journal of Molecular Sciences, 2020. Volume 22, Issue 1.

  • The information on this page is based on literature searches and specialist checking. We used many references and there are too many to list here. If you need additional references for this information please contact with details of the particular issue you are interested in.

Last reviewed: 
27 May 2022
Next review due: 
27 May 2022

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