Hypericaceae
Hypericum perforatum
St John's wort · Perforate St John’s-wort
- Part used
- aerialflower
- Native range
- Europe, western Asia and north Africa; an aggressive naturalised weed in Australia and North America
- Morphology
- Perennial to about eighty centimetres with paired leaves that appear perforated when held to the light — they are translucent oil glands — and five-petalled yellow flowers that stain the fingers red.
What is in it
Evidence
Cochrane reviews find it comparable to standard antidepressants for mild to moderate depression, with fewer side effects. Evidence in severe depression is weaker. The trials are dominated by German products and preparations vary considerably.
Safety
Photosensitivity, particularly in fair skin and at higher doses. Serotonin syndrome risk when combined with serotonergic drugs. The dominant hazard is not toxicity but interaction, and it is a serious one.
Interactions: Induces CYP3A4 and P-glycoprotein, lowering blood levels of many drugs; Failure of hormonal contraception; Loss of control in HIV on antiretrovirals; transplant rejection on ciclosporin; Reduced effect of warfarin, some anticonvulsants and some chemotherapy agents; Serotonin syndrome with SSRIs, SNRIs, triptans and tramadol
Regulatory: Available over the counter in Australia and much of Europe. Regulators including the TGA, MHRA and EMA have issued formal interaction warnings.
How the traditions classify it
Three systems, rating the same plant. Where they disagree, none of them is correcting the others — they are separate frameworks that arrived at their categories independently.
Historical use
In European practice since the classical period, principally as a wound herb and for melancholy. Its modern use for depression dates from mid-twentieth-century German practice.
Recorded as history and attributed where possible. Long use establishes that a plant was widely used, not that it worked, and not that it was safe.
Worth knowing
St John's wort created the field of herb-drug interactions more or less single-handedly.
Through the 1990s it was the most popular herbal antidepressant in the world, and then reports started arriving that could not be dismissed: transplant patients rejecting organs, people with HIV losing viral control, unplanned pregnancies. In 2000 the Lancet published the transplant findings and regulators moved within months.
The mechanism is the important part, because it is silent. Hyperforin induces the liver enzymes that clear other drugs, so the other drug is simply cleared faster and stops working. Nothing feels wrong. There is no reaction to notice. The medicine just quietly stops.
That it is genuinely effective is what makes it dangerous. An inert herb cannot do this.
Nomenclature verified against GBIF backbone taxonomy.