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St John's wort
St John's wort — what the European monograph actually supports, what it is not for, the form and how long it is meant to be used, side effects, and the 8 medicine interactions documented for it.
This is a reference page, not a diagnosis and not a prescription. Herbal products are real pharmacology: they have effects, side effects and interactions with medicines. Tell your doctor and your pharmacist everything you take, including teas and supplements, and never stop or change a prescribed medicine because of anything you read here.
What it is
Hypericum perforatum L. — flowering tops (Hyperici herba)
Local names across the region this site serves: naistepuna (ET) · mäkikuisma (FI) · зверобой (RU).
Grouped here under Mind, mood and fatigue. Regulatory position: EU herbal monograph — well-established use for specific dry extracts, plus traditional-use indications.
What the evidence supports
The registered indication: Mild to moderate depressive episodes, for particular standardised dry extracts; traditional-use preparations are also registered for temporary mental exhaustion and, externally, for minor wounds and skin inflammation.
This is the one herb on the list where "it works" and "it is genuinely dangerous" are both true, and the second is a consequence of the first. Meta-analyses of standardised extracts in mild to moderate depression compare favourably with placebo and, in several head-to-head trials, with standard antidepressants at similar effect and better tolerability. That evidence is why the EU monograph carries a well-established-use indication for defined dry extracts and why, in some countries, these are pharmacy medicines rather than shelf supplements. The danger is pharmacokinetic. Hyperforin, one of its constituents, is a strong inducer of the CYP3A4 enzyme family and of the P-glycoprotein transporter — between them the route by which an enormous share of prescription medicines is cleared from the body. Induction means the body disposes of the other drug faster, its blood level falls, and it stops doing its job. Every warning below comes from that single mechanism. The effect builds over one to two weeks and takes a similar time to fade after stopping, so the interaction runs in both directions in time: starting it lowers the other drug, stopping it lets the level climb back. Both changes belong with the prescriber, not with you.
A — Recognised efficacy A European Union herbal monograph carries a well-established-use indication for a defined preparation, meaning the regulator accepted clinical evidence.
What it is not for
Severe depression, bipolar disorder, and any depression with thoughts of self-harm. If you are having those thoughts, contact emergency services or a crisis line now — that is not a herbal question.
Form, strength and how long
Standardised dry extracts in tablets (the preparations the efficacy evidence concerns), teas and tinctures with far less predictable content, and an oil macerate used on the skin.
Duration. Antidepressant effects, if they come, take several weeks. Depression that does not respond, or deepens, needs reassessment rather than a longer course.
No gram figure appears on this page on purpose. The plant part, the extraction solvent and the drug-to-extract ratio together define a preparation, and a number taken from one does not describe another. The reasoning is set out on the hub; the amount that applies to you is the one printed on the pack you are holding, and a pharmacist will read it with you.
Side effects
Photosensitivity — the skin reacts more strongly to sun and to tanning beds, most noticeably in fair-skinned people on higher amounts. Stomach upset, restlessness, headache, dry mouth. Stopping abruptly after long use can cause a withdrawal-like unsettledness.
Who should avoid it
Not recommended in pregnancy or breastfeeding. Not for under-18s. And a rule with no exceptions: never start it while taking a prescribed medicine without checking with a pharmacist or doctor first.
Interactions with medicines
| Medicine or substance | What is described |
|---|---|
| Combined hormonal contraceptives | Breakthrough bleeding and contraceptive failure are documented, and the warning is a standing entry in the product information for combined hormonal contraceptives. This is the most consequential herb-drug interaction that can be bought over a shop counter without anybody asking a question. |
| SSRI and SNRI antidepressants | Two problems at once. St John's wort has serotonergic activity of its own, so combining it raises the risk of serotonin syndrome — agitation, sweating, tremor, fast heartbeat, confusion. It also induces the enzymes that clear some antidepressants, so their levels can fall. Never add it to a prescribed antidepressant on your own, and never stop a prescribed one to swap. |
| Anticoagulants and antiplatelets (warfarin, DOACs, aspirin, clopidogrel) | Warfarin control is lost as INR falls and clot risk rises, and levels of the direct oral anticoagulants drop. St John's wort is named explicitly in DOAC product information. |
| Immunosuppressants and transplant medicines | Transplant rejection has been reported in patients who started St John's wort while taking ciclosporin or tacrolimus. This is the most serious documented consequence of the interaction and the reason transplant teams ask about herbal products by name. |
| HIV and hepatitis C antivirals | Levels of HIV protease inhibitors and non-nucleoside reverse transcriptase inhibitors fall far enough to risk treatment failure and resistance. |
| Cancer and hormone-blocking treatment | Several oral cancer medicines are cleared by the same enzyme route, and falling levels mean less treatment than intended. |
| Statins | Simvastatin and atorvastatin levels drop, so cholesterol control quietly worsens. |
| Digoxin | Digoxin levels fall, which matters because digoxin has very little margin between too little and too much. |
The reverse view — start from the medicine rather than the plant — is in the medicine, food and alcohol interactions reference, and summarised for every herb on this site.
Sources: European Medicines Agency — Committee on Herbal Medicinal Products (HMPC), European Union herbal monographs · NIH National Center for Complementary and Integrative Health — herb fact sheets · checked 2026-09-06
Frequently asked questions
What is st john's wort used for?
Mild to moderate depressive episodes, for particular standardised dry extracts; traditional-use preparations are also registered for temporary mental exhaustion and, externally, for minor wounds and skin inflammation. This is the one herb on the list where "it works" and "it is genuinely dangerous" are both true, and the second is a consequence of the first. Meta-analyses of standardised extracts in mild to moderate depression compare favourably with placebo and, in several head-to-head trials, with standard antidepressants at similar effect and better tolerability. That evidence is why the EU monograph carries a well-established-use indication for defined dry extracts and why, in some countries, these are pharmacy medicines rather than shelf supplements. The danger is pharmacokinetic. Hyperforin, one of its constituents, is a strong inducer of the CYP3A4 enzyme family and of the P-glycoprotein transporter — between them the route by which an enormous share of prescription medicines is cleared from the body. Induction means the body disposes of the other drug faster, its blood level falls, and it stops doing its job. Every warning below comes from that single mechanism. The effect builds over one to two weeks and takes a similar time to fade after stopping, so the interaction runs in both directions in time: starting it lowers the other drug, stopping it lets the level climb back. Both changes belong with the prescriber, not with you.
Does st john's wort work?
Graded A here: A European Union herbal monograph carries a well-established-use indication for a defined preparation, meaning the regulator accepted clinical evidence. Severe depression, bipolar disorder, and any depression with thoughts of self-harm. If you are having those thoughts, contact emergency services or a crisis line now — that is not a herbal question.
How much st john's wort should I take?
This reference does not print gram figures, because they do not transfer between preparations of different extract strength. What can be said honestly is the form and the duration: Standardised dry extracts in tablets (the preparations the efficacy evidence concerns), teas and tinctures with far less predictable content, and an oil macerate used on the skin. Antidepressant effects, if they come, take several weeks. Depression that does not respond, or deepens, needs reassessment rather than a longer course.
What are the side effects of st john's wort?
Photosensitivity — the skin reacts more strongly to sun and to tanning beds, most noticeably in fair-skinned people on higher amounts. Stomach upset, restlessness, headache, dry mouth. Stopping abruptly after long use can cause a withdrawal-like unsettledness.
Does st john's wort interact with medicines?
Yes — documented for Contraceptives, Antidepressants, SSRIs, Anticoagulants, warfarin, Immunosuppressants, HIV medicines, Cancer treatment, Statins, Digoxin. Each one is described on this page, with a link to the medicine-side reference where one exists.
Others in mind, mood and fatigue
Ginkgo
Improvement of cognitive impairment and of quality of life in mild dementia, for a specific standardised leaf dry extract used under medical supervision.
Ginseng (Panax)
Symptoms of asthenia such as fatigue and weakness.
Rhodiola (roseroot)
Temporary relief of symptoms of stress, such as fatigue and a sensation of weakness.
Ashwagandha
Nothing a European regulator has assessed. It is marketed for stress, sleep, testosterone and athletic performance.
Keep the whole list in one place
TempoLife logs supplements alongside food, sleep and how you actually felt — so the answer to "what are you taking?" is a screen, not a guess.