The herbal medicine St John's wort is an extract from the flower St John's wort (Hypericum perforatum). It has been used for many years to treat mild to moderate depression.

Studies have show that St John's wort does have a beneficial effect in treating mild depression and it has the advantage of rarely causing any side effects, so it is usually quite safe to take. Similar to the antidepressants which are prescribed by doctors it takes two to three weeks to have any affect.

However, St John's wort can also interact and interfere with the action of a number of other drugs, such as some heart and epilepsy drugs, the contraceptive pill, antibiotics and others. So if you are taking any other medication check with your doctor before taking St John's wort.

Also, a small study has shown that St John’s wort reduces the effectiveness of a chemotherapy drug called irinotecan. When the patients in the study were given St John’s wort the amount of irinotecan in their blood was decreased. This means they received less chemotherapy than they needed to treat their cancer. People who are having or about to have chemotherapy should ask their doctor’s advice if they are taking St John’s wort.