The short answer
Garden cress changed phenytoin concentrations in a dog study, but its effect in people is unknown. Have concentrated Lepidium sativum products reviewed before use; animal findings do not establish a human dose, a toxicity rate or a safe spacing interval.
What this answer covers
Lepidium sativum preparations with oral phenytoin; tested animal exposure does not establish effects of ordinary food or all extracts.
- Supplement or preparation
- Garden cress
- Medication ingredient
- phenytoin
The direct experiment was in dogs
After a week of garden-cress treatment, the study found changes in phenytoin peak concentration, half-life and apparent clearance. No patients were studied, so the direction and size of a human effect remain unconfirmed.
Different herbs had different effects
The same paper evaluated other herbs separately. Their results were different and should not be combined into a single claim about every botanical. The garden-cress preparation also cannot define exposure from an unrelated extract or ordinary food serving.
Phenytoin levels require careful interpretation
Phenytoin has a narrow margin between adequate treatment and adverse effects, and its metabolism can respond nonlinearly to dose changes. A possible interaction should be assessed using the actual product, symptoms and drug-level monitoring where indicated.
There is no validated home adjustment
Do not change the medication dose to compensate for the supplement or assume a dosing gap prevents the concern. Discuss planned supplement changes with the prescriber and maintain the established phenytoin regimen while seeking advice.
Evidence and practical considerations
Absorption & effectiveness
Garden cress changed phenytoin concentrations in a dog study, but its effect in people is unknown. Have concentrated Lepidium sativum products reviewed before use; animal findings do not establish a human dose, a toxicity rate or a safe spacing interval.
- Exact scope
- Lepidium sativum preparations with oral phenytoin; tested animal exposure does not establish effects of ordinary food or all extracts. with Oral phenytoin; free-acid and sodium-salt formulations are explicitly distinguished.
- Medication form and route
- oral
What remains uncertain
- No universal risk rate or dose interval is established. Specific original-source limitations and access status are documented.
Factors that may matter: Exact preparation and amount; Medication formulation and drug levels; Seizure history and other treatments.
Read the supporting source summaries
Source 1: Current U.S. regulatory labeling
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People prescribed oral phenytoin for supported seizure indications.
Labels name folic acid and St John’s wort as possible causes of lower phenytoin levels. Calcium-carbonate and magnesium-hydroxide antacids should not be taken simultaneously. Abrupt withdrawal can worsen seizures.
How this applies: Exact medication precautions with the formulation bridge explicitly retained.
A generic mineral is not every antacid salt. Free-acid and sodium formulations have different drug content; oral absorption findings do not apply to intravenous administration.
Source 2: Original animal pharmacokinetic study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: Beagle dogs, not patients.
Garden cress modestly raised peak concentration and half-life and reduced apparent clearance.
How this applies: Nonclinical signal warrants product review but does not prove higher phenytoin levels in people.
Animal exposure; human effect, preparation-equivalent dose and clinical toxicity are unknown. Other herbs in the paper had different effects and are not substituted.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Initial source-checked research draft with exact formulation limits, contrary evidence and source-access details. Clinical review not recorded. | |
| Research summary published |
Article revision: 50a85b167ddae44f
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.