Interaction fact sheet
St John's wort and antidepressants
Combination to avoid: risk of serotonin syndrome.
St John's wort itself affects serotonin. Combined with an antidepressant, it can cause serotonin syndrome, which can sometimes be severe. Cases have been reported in older people combining the two.
In brief
- Mechanism
- St John's wort increases serotonin activity, as do SSRI and SNRI antidepressants. Their effects add up.
- Magnitude
- Reported cases of serotonin syndrome, including a series of 5 cases in older people.
- Who is affected
- People taking antidepressants: SSRIs, SNRIs and tricyclics, as well as those taking tramadol, triptans or lithium.
- What to do
- Do not combine them. Do not replace an antidepressant with St John's wort on your own.
Serotonin syndrome
When serotonin activity becomes excessive, the nervous system goes into overdrive. Signs usually appear within hours of combining the substances: agitation, confusion, sweating, tremors, muscle contractions, diarrhea, fever and a rapid heartbeat. Severe cases, with high fever and rigidity, are a medical emergency.
A case series published in 1999 describes 5 older people who had combined St John's wort with a prescription antidepressant, all with clinically diagnosed serotonin syndrome.
A double problem
St John's wort creates two problems at once. It adds its serotonergic effect to that of the antidepressant, and it speeds up the liver's clearance of many medicines. Depending on the treatment, it can therefore both increase the risk of adverse effects and reduce the effectiveness of other medicines.
Stopping an antidepressant to switch to St John's wort without professional support also carries a risk of withdrawal symptoms and relapse.
In practice
What you can do
- Don't combine St John's wort with an antidepressant.
- If you want to stop or change treatment, do it gradually with your doctor.
- Mention St John's wort whenever you get a new prescription.
When to seek advice
- Agitation, sweating, tremors, fever or a rapid heartbeat after combining substances: call 15.
- Wanting to stop or change your antidepressant.
- Suicidal thoughts: call 3114, free and available 24/7.
Main sources
- 01Lantz MS et al. St. John's wort and antidepressant drug interactions in the elderly. Journal of Geriatric Psychiatry and Neurology, 1999. PubMed
- 02Hall SD et al. The interaction between St John's wort and an oral contraceptive. Clinical Pharmacology & Therapeutics, 2003 (activation du CYP3A4). PubMed
Frequently Asked Questions (FAQ)
Can you take St John's wort with an SSRI?
No. The combination puts you at risk of serotonin syndrome. St John's wort also interacts with many other medicines.
How long should you wait between the two?
It depends on the antidepressant; some stay in the body for a long time. The switch must be managed with your doctor, who will set the waiting period.
What are the signs of serotonin syndrome?
Agitation, confusion, sweating, tremors, muscle jerks, diarrhea, fever and a rapid heartbeat. Cases with high fever and rigidity are an emergency.