St John’s Wort: Uses, UK Rules, Interactions and Side Effects

What is St John’s wort?

St John’s wort is a wild plant, Hypericum perforatum, with small yellow flowers that bloom around midsummer. Its flowering tops are dried and made into tablets, capsules, teas and tinctures. The main active compounds are hypericin and hyperforin, and hyperforin is the one mainly responsible for its many interactions with medicines.

It grows wild across the UK and has a long history in European folk medicine. Unlike most products on a health shop shelf, the St John’s wort tablets sold in UK pharmacies are regulated as medicines, not food supplements.

Is St John’s wort legal in the UK?

Yes. St John’s wort is legal to buy in the UK, and the products sold in pharmacies are registered herbal medicines under the MHRA’s Traditional Herbal Registration (THR) scheme. A THR means the MHRA has checked safety, quality and evidence of traditional use. It does not mean the product has been proven to work.

That registered wording belongs to the licensed medicine and its leaflet, not to us: we’re quoting it so you know what the label means. The MHRA’s own advice is that the effectiveness of a THR product hasn’t been assessed, only its safety, quality and history of use.

If you buy St John’s wort online, check for a THR number. Products sold without one, including some teas and imported capsules, may not carry the warnings you need about the pill and other medicines.

What is St John’s wort used for?

St John’s wort is mainly used for low mood. UK registered products are for slightly low mood and mild anxiety, based on traditional use only, and their leaflets say not to take them if you’ve been diagnosed with depression. Elsewhere in Europe, some doctors prescribe it for mild to moderate depression.

The UK leaflet we checked says the product does not relieve the symptoms of depression, and to talk to your doctor first if you think you may be depressed. The NHS says some people take it for depression, but it’s not recommended by doctors.

If low mood is what’s behind your search, our guides to low mood vs depression and the winter blues cover the signs, what helps and when it’s time to speak to someone. For prescribed options, see anxiety medication in the UK.

Does St John’s wort work? What the evidence says

Trials suggest some St John’s wort extracts work better than placebo for mild to moderate depression, and about as well as standard antidepressants over 4 to 12 weeks. But results vary by country and product, strengths differ between brands, and long-term evidence is thin. NICE advises doctors not to prescribe or advise it.

Most of this research is on depression, not anxiety. The extracts tested in trials were specific standardised products, so the results don’t automatically apply to any tablet, tea or tincture on sale. And the UK registered products are not meant for diagnosed depression at all.

Hyperforin, thought to drive part of its effect on mood, also speeds up the breakdown of many medicines. For other mood-related supplements and their safety, see saffron benefits, 5-HTP and tryptophan.

Which medicines interact with St John’s wort?

St John’s wort interacts with a long list of medicines, including all hormonal contraceptives, antidepressants, HRT, warfarin, epilepsy medicines, ciclosporin and tacrolimus, HIV medicines, digoxin, some statins, triptans, some blood pressure medicines, lithium and thyroxine. It can make some of them work less well, and with antidepressants it can cause dangerous side effects.

The leaflet also lists medicines not to take at the same time unless a doctor has said it’s safe, including some antibiotics (clarithromycin, erythromycin), some antifungals, omeprazole and lansoprazole, tramadol, gliclazide and anaesthetics. It also says to stop St John’s wort at least 10 days before an operation and tell the hospital you take it.

Never stop or change a prescribed medicine in order to take St John’s wort instead. And if you already take St John’s wort alongside another medicine, don’t stop it suddenly without speaking to your pharmacist or doctor, because stopping it can change the level of the other medicine in your blood too.

St John’s wort and the pill

St John’s wort can make hormonal contraception less effective, which means it may not prevent pregnancy. The MHRA advises women using hormonal contraception to prevent pregnancy not to take any product containing St John’s wort. That covers the combined pill, the mini pill, the implant, patches and emergency contraception.

The MHRA had received 19 Yellow Card reports of suspected interactions with hormonal contraceptives when it issued that warning, and 15 of them involved unplanned pregnancies, including four with contraceptive implants. If you’ve taken St John’s wort while relying on hormonal contraception, speak to a pharmacist or your GP or sexual health clinic about extra protection.

St John’s wort with sertraline and other antidepressants

Don’t take St John’s wort with sertraline or any other antidepressant. The NHS says not to use St John’s wort when taking sertraline, and the UK leaflet lists every main antidepressant. Together they can raise serotonin too far and cause serotonin syndrome, a rare but serious reaction.

iSigns include a fast heartbeat, sweating, shaking, twitching muscles and feeling confused or agitated: call NHS 111 straight away if you get these. For more on antidepressant side effects, see does sertraline cause insomnia? and does fluoxetine make you tired?

Asking about CBD and medicines instead? See can CBD interact with medication? For other herbs with medicine cautions, see ashwagandha side effects and lemon balm.

St John’s wort side effects

The most common St John’s wort side effects are stomach upsets, tiredness, restlessness, headache and dizziness. It can also make skin more sensitive to strong sunlight and sunbeds, causing sunburn-like reactions, especially in fair skin. If you get an allergic reaction such as a rash or hives, stop taking it and see a doctor.

• Stomach: indigestion, loss of appetite, feeling sick, diarrhoea or constipation.
• Nervous system: tiredness, restlessness, headache, nerve pain or tingling, dizziness, anxiety and, rarely, mania (raised excitability).
• Skin and light: the leaflet says to avoid excessive sunbathing and sunbeds while taking it.
• Driving: it may make you dizzy or sleepy; if it does, don’t drive or use machines.

Tell your pharmacist or doctor if a side effect is severe or lasts more than a few days. You can report suspected side effects from herbal medicines to the MHRA’s Yellow Card scheme.

Who should not take St John’s wort?

Don’t take St John’s wort if you’re under 18, pregnant or breastfeeding, have been diagnosed with depression, take any medicine on the interaction list, have very sun-sensitive skin or are having light treatment, or have an operation coming up. If you’re unsure whether any medicine you take is affected, ask a pharmacist first.

• Pregnancy and breastfeeding: the NHS says not to take it, because it isn’t known for sure to be safe.
• Diagnosed depression: UK registered products are not for depression; speak to your GP about treatment.
• Bipolar disorder: mania is a listed side effect, so speak to your doctor before any mood remedy.
• Light therapy: including a SAD lamp used as treatment; check with your doctor first.
• Surgery: stop at least 10 days before an operation, as the leaflet advises.
• Lactose intolerance: some tablets contain lactose; check the pack.

Women going through the menopause should also take care: the leaflet lists all HRT. Our guide to the best supplements for menopause covers what’s known for each option.

How much St John’s wort do you take?

Follow the pack of a registered product. The UK registered tablet we checked contains 250mg of dried extract, equal to 875 to 1,500mg of St John’s wort, taken once a day by adults. The leaflet says to talk to a pharmacist or doctor if symptoms worsen or don’t improve after 6 weeks.

iStrength varies a lot between products, which is one reason NICE gives for not recommending it. Don’t double up with teas or tinctures alongside tablets, and don’t take more than the pack says. Taking too many is a reason to speak to a pharmacist or doctor.

When to see a GP or get urgent help

See a GP if you’ve had a low mood for more than 2 weeks, you’re struggling to cope, or what you’re trying yourself isn’t helping, the NHS says. Adults can also refer themselves to NHS Talking Therapies without seeing a GP. Get urgent help if you feel you can’t keep yourself safe.

For men in particular, our men’s mental health guide lists where to get help in the UK.