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.  

Summary

• 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.

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.

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​ 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.

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. 

Safety of complementary and alternative therapies

This page is due for review. We will update this as soon as possible.