St. John's Wort

What is St. John’s Wort?

St. John’s wort is a yellow-flowered perennial native to Europe, western Asia and North Africa and now naturalised across temperate regions worldwide, where it is often considered a weed. The flowering tops, dotted with translucent oil glands and red-pigmented spots, are dried for tea, tincture and standardised extracts. It is one of the most widely used herbal remedies for low mood.

Traditional & Modern Uses

Traditionally the herb was used for nervous complaints and, as an infused oil, for wounds, burns and nerve pain (a vulnerary use). Today its best-known application is for mild to moderate depression, where standardised extracts have been studied as an alternative to conventional antidepressants. It is also used for anxiety and seasonal low mood.

Phytochemistry

Two compound classes dominate St. John’s wort. The red naphthodianthrone pigments hypericin and pseudohypericin — concentrated in the dark glands of the flowers — are the marker compounds to which extracts are standardised ^{1,2Reference 1Tian et al. · 2024Documentary Analysis of Hypericum perforatum (StView study →Reference 2Bagdonaitė et al. · 2012Variation in concentrations of major bioactive compounds in Hypericum perforatum L. from LithuaniaView study →}. The phloroglucinol hyperforin is now thought to carry much of the antidepressant effect, and also drives the herb’s powerful induction of drug-metabolising enzymes ^{1,2Reference 1Tian et al. · 2024Documentary Analysis of Hypericum perforatum (StView study →Reference 2Bagdonaitė et al. · 2012Variation in concentrations of major bioactive compounds in Hypericum perforatum L. from LithuaniaView study →}. These sit alongside a rich flavonoid fraction — the biflavones amentoflavone and biapigenin plus hyperoside, quercetin, rutin and kaempferol — and astringent tannins ^{2Reference 2Bagdonaitė et al. · 2012Variation in concentrations of major bioactive compounds in Hypericum perforatum L. from LithuaniaView study →}.

Constituent Summary

Figures are percent of dried herb and vary with chemotype, harvest time and drying; products are typically standardised to ~0.3% hypericins or to hyperforin content ^{1,2Reference 1Tian et al. · 2024Documentary Analysis of Hypericum perforatum (StView study →Reference 2Bagdonaitė et al. · 2012Variation in concentrations of major bioactive compounds in Hypericum perforatum L. from LithuaniaView study →}. Entries marked No Data are documented qualitatively only.

Safety

St. John’s wort is pharmacologically active and carries some of the most clinically important interactions of any herb. It induces liver enzymes (notably CYP3A4) and acts on serotonin, which means it can reduce the effectiveness of many medications — including hormonal contraceptives, anticoagulants, immunosuppressants and certain HIV and cancer drugs — and can cause dangerous serotonin excess if combined with antidepressants. It also causes photosensitivity, increasing the risk of sunburn. Anyone taking prescription medication should consult a clinician before using it, and it should not be combined with other antidepressants. Avoid in pregnancy.

References

1. Tian, J., et al. (2024). Documentary Analysis of Hypericum perforatum (St. John’s Wort) and Its Effect on Depressive Disorders. Pharmaceuticals, 17(12), 1625. doi:10.3390/ph17121625
2. Bagdonaitė, E., Mártonfi, P., Repčák, M., & Labokas, J. (2012). Variation in concentrations of major bioactive compounds in Hypericum perforatum L. from Lithuania. Industrial Crops and Products, 35(1), 302–308. doi:10.1016/j.indcrop.2011.07.018