St John's wort for depression: what the evidence says and the risks

St John's wort is a plant with yellow flowers. Cancer Research UK explains that the herbal remedy is made from the flowers and unopened buds, that its scientific name is Hypericum perforatum, and that it is also known as hypericum or goatweed. It is sold as capsules, tablets, powder, tinctures, liquid extract, tea bags and creams.

People use it mainly for low mood. The NHS describes it as a herbal treatment that some people take for depression, available from health food shops and pharmacies. Because it is sold over the counter, it can feel like a gentle, natural choice, but the plant contains active compounds that change how the body handles other medicines, which is why it needs more care than many people expect.

Cancer Research UK says two of the active ingredients, hypericin and hyperforin, may change the activity of neurotransmitters, the chemical messengers in the brain that scientists believe play a part in depression. That is a proposed mechanism rather than a settled explanation of how the remedy works.

The two UK sources read for this page describe the evidence in slightly different tones. The NHS says there is some evidence that St John's wort may help less severe depression but that it is not recommended by doctors. Cancer Research UK says several studies, including large randomised trials, compared certain extracts with placebo and with standard antidepressants, and that much of that research suggests the extracts help mild to moderate depression.

Cancer Research UK also reports that a 2016 systematic review concluded St John's wort can help with mild to moderate depression, while noting that more studies are needed in severe depression and that there were limitations in the studies, including incomplete reporting of side effects.

The practical difficulty is product variation. The NHS points out that active ingredients vary between individual brands and batches, so you can never be sure what effect a particular product will have. Results from a trial of one standardised extract therefore do not necessarily apply to whatever capsule is on a shop shelf.

The main safety concern is drug interactions. Cancer Research UK says St John's wort can change how well some drugs work, making them either stronger or weaker, and that it does not list every interaction. The medicines it names include some cancer drugs, ciclosporin and tacrolimus, warfarin and other blood thinners, some antibiotics, theophylline, digoxin, some epilepsy and HIV drugs, oxycodone, contraceptives and some antidepressants.

The NHS also advises that St John's wort should not be taken in pregnancy or while breastfeeding because it is not known to be safe, and that it can interact with the contraceptive pill, reducing its effectiveness. More generally, the NHS says herbal medicines are not recommended for children and should not be taken if you have kidney or liver problems or take certain medicines, and that you should check with a pharmacist first.

Cancer Research UK describes side effects as uncommon and usually mild. They include headaches, constipation, stomach upsets, sleep disturbances, dizziness, tiredness, dry mouth, skin rash and increased sensitivity to sunlight. It advises avoiding strong sunlight, tanning beds and skin laser treatment where sensitivity is a concern.

If you do use a product, both sources point to the same safeguard. Cancer Research UK says that in the UK it is important to buy only products registered under the traditional herbal registration scheme, which carry a THR symbol and have been tested for quality and safety. The NHS gives the same check and warns that unlicensed products bought online may not be safe.

It is worth telling every doctor, nurse or pharmacist treating you that you take it. The NHS asks people to do this for any herbal medicine, and it also warns against stopping any prescribed medicine without speaking to your doctor first.

The NHS depression treatment page sets out options by severity. For mild depression it describes watchful waiting with a review after 2 to 4 weeks, guided self-help (usually 6 to 8 sessions based on CBT principles), exercise, and talking therapies, which you can access through a GP or by referring yourself to an NHS talking therapies service.

For moderate to severe depression it lists antidepressants prescribed by a doctor, sometimes combined with talking therapy because the combination usually works better than either alone, and referral to a mental health team for severe depression. CBT, according to the NHS, usually involves sessions weekly or fortnightly over 8 to 16 sessions.

If low mood is persistent, affects daily life or you are having thoughts of harming yourself, the NHS advice is to speak to a GP. In an emergency, call 999 or go to A&E, and NHS 111 can advise when you are unsure where to turn.

For many people the sensible approach is to treat St John's wort as a medicine rather than a food supplement: discuss it with a pharmacist, check every other tablet you take, choose a registered product and tell the GP. If low mood has lasted more than a couple of weeks, a proper assessment matters more than the choice of remedy.

This page is general information and does not recommend any product. It cannot account for your own medicines or health history, which is why the NHS repeatedly points people to a pharmacist or GP before starting a herbal medicine.