St John's Wort 💊
⚠️ Key Point: St John’s Wort is a CYP3A4 inducer.
It can render other drugs less effective ➝ risk of treatment failure.
Always check the BNF for up-to-date prescribing advice.
💊 About
- Derived from the plant Hypericum perforatum.
- Used as a herbal remedy for mild to moderate depression.
- Not recommended in standard clinical practice due to safety and interaction profile.
⚙️ Mode of Action
- Exact mechanism unclear.
- Likely involves inhibition of serotonin, dopamine, and noradrenaline reuptake.
- Potent inducer of CYP3A4 and P-glycoprotein ➝ accelerates metabolism of many drugs.
📋 Indications / Dose
- OTC preparations for mild to moderate depression (variable strength, not standardised).
- Not licensed as a conventional antidepressant in the UK.
🔄 Interactions
- ⬇️ Drug levels and efficacy due to increased metabolism:
- Digoxin
- Theophylline
- Ciclosporin
- Oral contraceptives (risk of contraceptive failure)
- Warfarin (reduced anticoagulant effect)
- SSRIs (e.g. sertraline) – risk of serotonin syndrome
⚠️ Cautions
- Major risk of treatment failure when co-prescribed with narrow therapeutic index drugs (e.g. ciclosporin, warfarin, digoxin).
- May cause serotonin syndrome if combined with SSRIs, SNRIs, or TCAs.
- Not suitable for use in place of prescribed antidepressants without medical supervision.
⛔ Contraindications
- See BNF for full details.
- Avoid with other antidepressants (risk of serotonin syndrome).
- Avoid in patients on critical therapies metabolised by CYP3A4.
⚡ Side Effects
- Headache, dizziness, drowsiness, restlessness.
- Gastrointestinal upset.
- Skin photosensitivity (increased sunburn risk).
- Mood swings, irritability.
- Serotonin syndrome if combined with SSRIs or TCAs.
📚 References
- BNF – St John’s Wort
- MHRA Drug Safety Update – Interactions with St John’s Wort.
- NICE Guidance – Depression in adults (NG222).
