St John's wort (Hypericum perforatum) is a yellow-flowered plant whose extract is sold worldwide as a herbal antidepressant. In Germany it is more commonly prescribed for mild depression than SSRIs. In the United States it is sold over the counter and treated as a dietary supplement. It is one of the most studied — and most medically important — herbal interactions in pharmacology, and that matters a great deal for people on antipsychotics.
St John's wort is a potent inducer of CYP3A4 and other drug-metabolising pathways, and it can substantially lower the blood levels of many antipsychotics — sometimes enough to cause symptom relapse — so it should not be combined with antipsychotic medication without prescriber guidance.
Why St John's wort matters pharmacologically
St John's wort contains hyperforin and several other active compounds. Hyperforin activates the pregnane X receptor (PXR), which in turn upregulates expression of CYP3A4, CYP2C9, CYP2C19, and the drug transporter P-glycoprotein. The effect is broad and clinically important. It typically takes 10 to 14 days to develop after starting the supplement and another 1 to 2 weeks to fade after stopping.
The NIH National Center for Complementary and Integrative Health maintains a clear summary of St John's wort interactions, including a long list of medications affected.
Antipsychotics most affected
Any CYP3A4-metabolised antipsychotic can have lower levels with concurrent St John's wort:
- Quetiapine — significantly lower levels possible
- Lurasidone — strongly affected; the FDA Latuda label warns about strong CYP3A4 inducers
- Lumateperone — the FDA Caplyta label notes that strong CYP3A4 inducers reduce exposure
- Ziprasidone — partly CYP3A4-metabolised
- Pimozide — CYP3A4 substrate; combination is risky for relapse
- Iloperidone — affected by CYP3A4 induction
- Cariprazine — primarily CYP3A4-metabolised; significantly lower levels possible
- Aripiprazole and brexpiprazole — CYP3A4 contributes; modest to moderate effect
- Clozapine — partly CYP3A4; modest effect possible
Risperidone, paliperidone, and olanzapine are less affected because their primary metabolism is through different pathways (CYP2D6, renal clearance, CYP1A2 respectively). Even so, St John's wort can affect them indirectly through P-glycoprotein and should not be combined casually.
The clinical implication: relapse
The most important risk is not toxicity but the opposite — relapse. If a patient on a stable antipsychotic dose starts taking St John's wort, the antipsychotic level can fall by 30 to 50%, sometimes more. For someone whose stability depends on staying within a therapeutic range, this can be enough to lose ground over weeks. The reverse is also true: stopping St John's wort can raise levels and produce side effects.
Several published case reports describe relapse of psychotic symptoms in patients who started St John's wort while on antipsychotic medication. Pharmacology references including Stockley's Drug Interactions list this as a clinically significant interaction.
Why people consider it
People on antipsychotics often experience depressive symptoms — these are common in schizophrenia, in schizoaffective disorder, and as side effects of medication. St John's wort is often suggested as a "natural" alternative to prescription antidepressants. The intention is reasonable. The execution can be harmful.
If depression is a problem, a prescriber-managed option is much safer. Many SSRIs and SNRIs combine well with most antipsychotics with manageable interactions. See SSRIs and antipsychotics.
Other interactions worth knowing
St John's wort lowers the effectiveness of many other medications, including:
- Hormonal contraceptives — pregnancy risk rises
- HIV medications — viral load can rise
- Warfarin — INR can drop
- Immunosuppressants like cyclosporine — transplant rejection has been reported
- Many anti-seizure drugs — levels fall
St John's wort can also raise serotonin and combine with SSRIs to produce serotonin syndrome — a potentially serious reaction. Combining St John's wort with SSRIs should be avoided.
You notice a return of voices, paranoia, or other symptoms after starting any new herbal supplement, or unusual restlessness, sweating, fever, or muscle twitching after combining herbal products with antidepressants — possible serotonin syndrome.
Practical questions to ask your prescriber or pharmacist
- If I am thinking about St John's wort, what would it do to my current medications?
- If depression is the reason, what prescriber-managed options are safer?
- Should I wait two weeks after stopping St John's wort before starting any new prescription?
- Are any other supplements I am taking acting as enzyme inducers?
The bottom line
St John's wort is a clear case where "natural" does not mean "safe in combination." For people on antipsychotic medication, the interaction risk is high enough that most clinical pharmacology references list it among the supplements to avoid. If depressive symptoms are a problem, a prescriber-managed plan that may include adjusting the antipsychotic, adding a compatible antidepressant, or considering CBT for depression is much safer than starting an over-the-counter inducer that can quietly undermine the medication keeping you stable.
This article is for educational purposes only and is not medical advice, diagnosis, or treatment. Always consult a qualified mental health professional. If you or someone you know is in crisis, call or text 988 in the US, or your local emergency number.