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St John’s wort

St John’s wort is a herbal remedy used as a complementary therapy for mild to moderate depression.

St John’s wort is a plant with yellow flowers. Other names for this herb 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 of the same name. 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.

St John’s wort has been used for hundreds of years for many health conditions, but there is currently no scientific evidence that it works to help with:

  • anxiety
  • tiredness (fatigue)
  • pre menstrual symptoms
  • difficulty sleeping
  • malaria
  • kidney problems
  • stomach problems
  • nerve pain
  • skin wounds and burns (used as a balm)

Why people with cancer use St John’s wort

About 25 out of every 100 people with cancer get depressed soon after they are diagnosed or after finishing their treatment.

It is quite normal to feel this way. It is not surprising that people who have cancer and feel very sad look for ways to help treat their depression. The press has often reported St John’s wort as a wonder drug to treat depression and help people to feel better.

Many people also 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 it 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.

What taking St John’s wort involves

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 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 mark and symbol on the packaging. THR products have been tested for quality and safety.

Possible 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

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 St. John's wort.

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.

It can interact with these groups of drugs and affect how well they work:

  • cancer drugs such as irinotecan, docetaxel and imatinib
  • ciclosporin (a drug to prevent organ transplant rejection)
  • blood thinning drugs such as warfarin
  • drugs to treat diarrhoea, such as loperamide hydrochloride
  • an asthma medicine called theophylline
  • heart medications such as digoxin
  • some epilepsy drugs
  • some HIV drugs

Research is also being carried out to find out if St John’s wort interacts with other drugs, such as strong painkillers.

You can have some very serious side effects if you take St John’s wort with these drugs. 

St John’s wort can interact with other types of anti depressants. It can increase the activity of a chemical called serotonin in your brain. This can cause confusion, hallucinations, sweating, feeling and being sick and a high temperature (fever).

St John's wort can make contraceptives work less well. This includes the pill and injectable hormone contraceptives. This can increase the risk of having an unplanned pregnancy.

St John’s wort can make you feel very drowsy if you take it with alcohol, drugs to help you sleep, strong painkillers or some sedatives.

If you are planning to take St John’s wort, it is very important to talk to your doctor first and let them know if you are taking any medicines or herbal supplements.

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

The Cochrane Collaboration pulls all the results of related trials together. It looked at all the trials that have used St John’s wort as a treatment for depression.  It says that extracts of St. John's wort are prescribed widely to treat depression. They seem to work as well as standard anti depressants for treating mild to moderate depressive symptoms. Side effects are mild and not common. But it does not seem so helpful for treating major depression.

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 (listed in the section above)

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 a week 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.

St John's wort isn’t very expensive and usually costs between £3 and £7 for 60 capsules. The prices can vary quite a lot if you buy it online.

Useful organisations

Contact any of these organisations for more information about the safety of using St John’s wort.

A UK based centre that offers a programme of complementary care (The Bristol Whole Life Approach) to people with cancer and their loved ones. They can give you information about appropriate, balanced and nutritious diets for people with cancer.

Chapel Pill Lane
BS20 0HH

Helpline: 0303 3000 118 (Mon to Fri, 9.30am to 5pm)

The ICNM can give information about herbal medicines. There is a list of practitioners on their website.

32–36 Loman Street

Phone: 0207 922 7980

Last reviewed: 
13 Jan 2015
  • Hyperforin a constituent of St John's wort (Hypericum perforatum L.) extract induces apoptosis by triggering activation of caspases and with hypericin synergistically exerts cytotoxicity towards human malignant cell lines.
    K Hostanska and others
    European Journal of Pharmaceutics and Biopharmaceutics. 2003 Volume: 56 Issue:1

  • Safety of St. John's Wort extract compared to synthetic antidepressants.
    V Schulz
    Phytomedicine. 2006, Volume 13: Issue: 3

  • Effect of St John's wort on imatinib mesylate pharmacokinetics.
    RF Frye and others.
    Clinical Pharmacology Therapeutics. 2004. Volume:76 Issue:4

  • St John's wort for depression: meta-analysis of randomised controlled trials.
    K Linde and others
    British Journal of Psychiatry.2005 Volume:186

  • Safety and efficacy of herbal sedatives in cancer care.
    KI Block and others
    Integrative Cancer Therapies. 2004 Volume 3, Issue 2

  • 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.

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