St John's wort | Cancer Research UK
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What St John’s wort is

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 other health conditions but there is currently no scientific evidence that it works for them. They include

  • Anxiety
  • Tiredness (fatigue)
  • Pre menstrual symptoms
  • Stomach problems
  • Difficulty sleeping
  • Malaria
  • Kidney problems
  • Skin wounds and burns (used as a balm)
  • Nerve pain

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. 

We have information about depression in people with cancer.

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. We have information about treatment for depression.

You may also find it helpful to read the following sections from our complementary therapy section


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.


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. You can see this review on St John’s wort and depression on The Cochrane Library website. 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. 

You can see a list of the current trials investigating St John’s wort on the National Centre for Complementary and Alternative Medicine (NCCAM) website.

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.


Side effects of St John’s wort

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

  • Stomach upsets
  • Increased sensitivity to sunlight
  • Tiredness
  • Dizziness
  • Headaches
  • Constipation
  • Sleep disturbances
  • A dry mouth

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.

If you are taking St John’s wort, 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.


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 know that St John's wort can interact with these groups of drugs and may affect how well they work

  • Cancer drugs such as irinotecan, docetaxel and imatinib
  • Some HIV drugs
  • Some epilepsy drugs
  • Blood thinning drugs such as warfarin
  • Heart medications such as digoxin
  • Drugs to treat diarrhoea, such as loperamide hydrochloride
  • An asthma medicine called theophylline
  • Ciclosporin – a drug to prevent organ transplant rejection

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.


Who shouldn’t use St John’s wort?

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 of the medicines listed in the section about the drugs St John’s wort may affect

You should not take St John’s wort if you are pregnant as 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.

If you are going to have an anaesthetic you need to stop taking St John’s wort at least a week before your surgery.


The cost of St John’s wort

The cost varies depending on

  • The dosage
  • The amount you buy
  • Where you buy it (health food shops, chemist or online)

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


Useful organisations

For more information about the safety of using St John’s wort, contact

Penny Brohn Cancer Care (formerly the Bristol Cancer Help Centre )
Chapel Pill Lane
Phone: 0845 123 23 10

This centre is staffed by doctors, nurses and therapists working in complementary medicine. They can provide information about complementary treatments, alternative diets, holistic medicine, counselling and relaxation.

The Institute for Complementary and Natural Medicine (ICNM)
32–36 Loman Street
Phone: 0207 922 7980

Can give information about herbal medicines and has a list of practitioners on their website.

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Updated: 13 January 2015