One of our products, Sleep Support, contains St John's Wort. This post exists because of that, not despite it.
What St John's Wort does to other medicines
St John's Wort is a liver enzyme inducer. It speeds up several cytochrome P450 enzymes — CYP3A4 particularly, and also 1A2 and 2C9 — which are the enzymes your body uses to clear a long list of medications.
Speed those up and the drug clears faster. The drug clears faster and its blood level falls. The blood level falls and the medicine stops working as well.
That's the whole mechanism, and it's why "natural" has no bearing on it. An enzyme inducer is an enzyme inducer. We have written separately about what the efficacy evidence for St John's Wort actually shows, and why we are cautious about it.
The anticonvulsant interaction
Medicines regulators name carbamazepine, phenobarbitone and phenytoin — reduced blood levels, with the risk of breakthrough seizures in someone whose epilepsy was previously controlled.
That's the interaction that matters most on this page, because the consequence is not a milder effect. It's a seizure in someone who wasn't having them. Our separate piece on what the evidence does and doesn't support in epilepsy covers the wider picture.
If you take any anticonvulsant, do not take St John's Wort — in our product or any other — without talking to your neurologist or pharmacist first.
The rest of the list
The same enzyme induction affects:
- Hormonal contraception — reduced effectiveness
- Warfarin — reduced anticoagulant effect
- Ciclosporin and tacrolimus — there are published case reports of transplant rejection
- Digoxin — loss of rhythm or heart-failure control
- HIV protease inhibitors — loss of viral suppression
And separately, through serotonin rather than enzymes:
- SSRIs and other antidepressants — increased serotonergic effects
- Triptans — sumatriptan, naratriptan — adverse serotonergic reactions
That last one is worth flagging on its own. If you take a triptan for migraine and you're looking at a sleep product, check the label. Ours contains both St John's Wort and 5-HTP.
What we're doing about it
Our product page and label warn about contraception, blood thinners, antidepressants, HIV medication and anti-rejection drugs. Anticonvulsants and triptans were not on that list. They have now been added. We keep a single page covering how our products interact with mental health medication, which is the place to start if you take anything prescribed.
We found this while mapping out what to write about epilepsy, which is a fairly good argument for doing that mapping.
If you already take both
Don't stop your anticonvulsant. Don't panic. Do speak to your pharmacist or prescriber — they can check whether your levels need testing, and stopping St John's Wort has its own effects on drug levels that are better managed than improvised.
Why this is on a supplement company's website
Because we sell the ingredient. A brand that publishes twenty posts on why its formulas work and none on how they interact isn't being cautious, it's being selective. Interaction risk is part of the evidence, and the evidence is the thing we said we'd lead with.
Interaction data drawn from published regulator guidance. This article is not medical advice — speak to your pharmacist or prescriber about your own medication.