Written by Karen Pilkington, Edzard Ernst and the CAM-Cancer Consortium.
Updated September 21, 2016

St. John's wort (Hypericum perforatum)

Is it safe ?

Adverse events

Numerous studies of St. John’s wort as an anti-depressant suggest that the adverse effects of oral St. John’s wort at recommended doses to treat depression are minimal and rare ranging in frequency from 0.1% to 2.4% 25-26. However, the safety of St John’s wort products taken as self-treatment without supervision by a healthcare professional requires further study. A small number of studies exploring the effects of self-treatment with St. John’s wort products report adverse effects including psychological symptoms, allergic reactions and visual disturbances, which participants believed to be related to the use of St. John’s wort 4.


Photosensitivity, allergy, pregnancy and lactation.


St. John’s wort powerfully interacts with a wide range of drugs, including some cancer medications 27,36 e.g. topoisomerase II cancer chemotherapy, cyclosporine, tacrolimus, amitripyline, irinotecan , digoxin, oral contraceptives or HIV-protease inhibitors. The mechanisms of these interactions include an induction of cytochrome P-450 microsomal oxidase enzymes (e.g. CYP3A4, CYP1A2, CYP2C9 , CYP2C19) and P-glycoprotein transporter pathway 28-30. The effect can lead to clinically relevant effects in cancer patients 31-32.


The elimination half-life of hypericin is about 24 to 27 hours. Repeated doses have been reported to lead to a steady state concentration after 4 days 1.

Other problems

There is an abundance of St. John’s wort preparations and only some are of high quality.  Commercial products should adhere to Good Agricultural Practice (GAP), Good Manufacturing Practice (GMP) and in Europe to the European guidelines “Quality of Herbal Medicinal Products”.

Citation Karen Pilkington, Edzard Ernst, CAM-Cancer Consortium. St. John's wort (Hypericum perforatum) [online document]. http://ws.cam-cancer.org/The-Summaries/Herbal-products/St.-John-s-wort-Hypericum-perforatum. September 21, 2016.


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