St John's Wort: Benefits, Interactions and What the Evidence Shows

St John's Wort (Hypericum perforatum) has more high-quality clinical evidence for depression than any other herbal medicine — a 2008 Cochrane meta-analysis of 29 RCTs (5,489 participants) found it significantly superior to placebo and comparable to standard antidepressants for mild-moderate depression, with fewer side effects. It is the most prescribed natural antidepressant in Europe, particularly Germany where it outsells pharmaceutical antidepressants for mild depression.

Clinical Evidence

The Cochrane 2008 review is the definitive evidence base: 29 trials, over 5,000 participants, finding St John's Wort equivalent to tricyclic antidepressants and SSRIs for mild-moderate depression with significantly fewer side effects. The advantages over antidepressants: no sexual dysfunction, minimal weight gain, no emotional blunting, and much lower rates of discontinuation due to side effects. Works best for mild-moderate depression; evidence for severe depression is weaker and it should not be used as sole treatment for severe depression.

How It Works

Hypericin and hyperforin — the two primary active compounds — inhibit the reuptake of serotonin, dopamine and norepinephrine (similar to antidepressants), have MAO-inhibitory activity, and modulate GABA and glutamate signalling. Hyperforin also activates the pregnane X receptor (PXR), which is responsible for its drug interactions.

Critical Drug Interactions — Read Before Using

St John's Wort induces CYP3A4 and P-glycoprotein — drug metabolism enzymes that process a large proportion of medications. This significantly reduces blood levels of many drugs, potentially causing treatment failure:

• Contraceptive pill: Can reduce effectiveness to sub-therapeutic levels, causing unintended pregnancy
• Antiretrovirals (HIV medication): Can cause treatment failure
• Cyclosporine (immunosuppressant): Multiple documented organ rejection cases from reduced levels
• Warfarin: Reduces anticoagulant effect, increasing clotting risk
• Certain antidepressants: Do not combine with SSRIs or SNRIs — risk of serotonin syndrome
• Some statins, certain antibiotics, digoxin

Always consult a pharmacist or doctor before starting St John's Wort if you take any medications.

Dose

Standardised extract: 300mg three times daily (900mg total), standardised to 0.3% hypericin and 3-5% hyperforin. Allow 4-8 weeks for full antidepressant effect — same timeline as pharmaceutical antidepressants. Do not stop abruptly after long-term use — taper over 2-4 weeks.