Fexofenadine and St John's Wort: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
St John's Wort
No brand names on recordFexofenadine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Decreased fexofenadine exposure and effectiveness
Interaction Deep Dive
In a systematic review of studies concomitant use of St John's wort with fexofenadine resulted in an increase in fexofenadine clearance and a decrease in fexofenadine Cmax and AUC with products containing hyperforin dosages of 3.3 to 7.5 mg/day. The risk of interactions cannot be excluded even for low-dose hyperforin St. John’s wort products, however the use of products that result in a dose of not more than 1 mg hyperforin per day may minimize the risk of interactions1.
Why it happens (mechanism)
Induction of P-glycoprotein (ABCB1) efflux transport of fexofenadine by St. John's wort
Literature reports
1 report — tap to read
a) In a systematic review of studies of pharmacokinetic interactions involving St John's Wort, concomitant use with fexofenadine in 3 studies resulted in a 48% to 102% increase in fexofenadine clearance (hyperforin dosage not specified), a 10% decrease in fexofenadine AUC with products containing a hyperforin dosage of 3.3 mg/day, and a 39% decrease in fexofenadine Cmax with products containing hyperforin dosages of 7.5 mg/day 1.
Common questions
Can I take Fexofenadine and St John's Wort together?
Decreased fexofenadine exposure and effectiveness Always confirm with your pharmacist or prescriber before making any change.
How serious is the Fexofenadine and St John's Wort interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "established". Well documented — supported by controlled studies or strong clinical data.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Fexofenadine or St John's Wort need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (1)
- Chrubasik-Hausmann S, Vlachojannis J, & McLachlan AJ: Understanding drug interactions with St John's wort (Hypericum perforatum L.): impact of hyperforin content. J Pharm Pharmacol 2019; 71(1):129-138.
Keep reading about St John's Wort
Keep reading about Fexofenadine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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