This information is for children and young people with depression. It tells you about St. John's wort. It is based on the best and most up-to-date research.
Does it work?
We don't know. There's some research that shows this herbal medicine can help adults with mild or moderate depression. But there isn't any evidence to show whether it works for children and teenagers or that it's safe for them. There's also a risk that St. John's wort can make some other medicines work less well.
What is it?
St. John's wort is a plant. Its scientific name is Hypericum perforatum. It has been used in Europe as a herbal remedy for depression for many years. It comes as a tablet that has concentrated extracts from the plant. But exactly how much is in the tablets varies from brand to brand.
In the UK, St. John's wort is sold as a food supplement, not as medicine. This means it hasn't been tested for safety in the same way as medicine.
The National Institute for Health and Clinical Excellence (NICE) is the government body that decides which treatments should be available on the NHS. It says that St. John's wort shouldn't be used for treating children or teenagers with depression. 
To read more, see NICE guidelines on depression in children and teenagers.
How can it help?
We don't know if it can help. We didn't find any research to show if St. John's wort helps children and teenagers with depression. There's some evidence that adults with mild or moderate depression feel better if they take it.  But we can't assume this treatment will work the same in younger people. 
How does it work?
No one knows for sure. There are two ideas about how St. John's wort might work. 
It may boost the level of chemicals in the brain called neurotransmitters. These carry signals between brain cells, and they don't work properly if you're depressed.
Depressed people have more of some hormones. St. John's wort may lower levels of these hormones.
Can it be harmful?
We didn't find any research on the side effects of St. John's wort in children and teenagers. In adults, common side effects seem to be stomach problems (such as sickness or diarrhoea), dizziness or confusion, tiredness and a dry mouth. Some people also said they got headaches or didn't enjoy sex as much when they were taking St. John's wort.  
The biggest problem with St. John's wort is that it interferes with lots of other medicines.    For example, you shouldn't take St. John's wort if you are taking:  
The contraceptive pill. St. John's wort makes the pill less effective, so there is a higher chance you'll get pregnant
Drugs for migraine called triptans, such as sumatriptan (brand name Imigran) and eletriptan (brand name Relpax)
Drugs for epilepsy
Warfarin, and similar drugs used to prevent blood clots
A drug for eczema called tacrolimus (brand name Protopic)
Drugs for HIV called indinavir, efavirenz, and nevirapine
St. John's wort interferes with lots of other drugs too. You should always tell your doctor if you are taking St. John's wort.