The short answer
Do not add St John’s wort to primidone without specialist review. The exact UK primidone label lists this combination as contraindicated because primidone levels and effectiveness may decrease.
What this answer covers
Hypericum perforatum preparations with oral primidone; not assumed equivalent to phenobarbital-only treatment.
- Supplement or preparation
- Hypericum perforatum
- Medication ingredient
- primidone
The exact label names this herb
The primidone product information specifically identifies St John’s wort and warns of reduced primidone concentrations and lack of efficacy. This is more specific than a general herbal warning.
Know which risk is being discussed
The concern is loss of treatment effect. The label does not establish that this pair causes additive sedation, serotonin toxicity or a particular rate of seizures.
Starting and stopping require a plan
Tell the prescriber if you already take St John’s wort. Do not adjust primidone yourself or assume that a few hours between doses prevents an enzyme-related interaction.
Keep the prescribed medicine steady
Do not stop primidone abruptly or adjust its dose to compensate for a supplement. Sudden withdrawal can provoke serious seizures. Tell the prescriber about new or worsening symptoms and all supplement changes.
Evidence and practical considerations
Absorption & effectiveness
Exact label supports avoiding co-use because reduced primidone exposure can undermine treatment; the relevant safety concern is treatment failure, not established additive sedation.
- Exact scope
- Hypericum perforatum preparations with oral primidone; not assumed equivalent to phenobarbital-only treatment. with Exact oral primidone; parent and metabolites distinguished; no other drug/route assumed equivalent.
- Medication form and route
- oral supplement unless pregnancy section explicitly distinguishes neonatal injection
- Timing or duration
- Preparation, dose and duration determine applicability; chronic nutrition evidence is not a single-dose interaction.
What remains uncertain
- No exact clinical effect magnitude or safe extract/spacing threshold identified. Starting and stopping an inducer require clinician review.
Factors that may matter: exact supplement identity; dose; other medicines; clinical indication; baseline nutrition; pregnancy where relevant.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People prescribed oral primidone for epilepsy.
Primidone itself and its phenobarbital and PEMA metabolites have anticonvulsant activity. Drowsiness, ataxia and vertigo can occur. Rare megaloblastic anemia may respond to folic acid without stopping therapy. Label advises maternal vitamin K1 around delivery. Abrupt withdrawal can provoke status epilepticus.
How this applies: Exact RxCUI 8691 IN primidone, UNII 13AFD7670Q, oral tablets.
Parent and metabolites are distinct active exposures. Pregnancy label advice is not proof of benefit for routine prenatal vitamin K or a general adult supplement requirement.
Source 2: current product label
medicines.org.uk · Source check Sep 10, 2026
Population: Patients receiving oral primidone for epilepsy or essential tremor.
Potent CNS depressant; long-term vitamin D supplementation may be needed. Lists folates among co-treatments requiring attention; megaloblastic anemia can respond to folic acid/B12. St John’s wort is listed under contraindicated co-use because primidone concentrations and effectiveness may decrease. Maternal vitamin K1 is advised near delivery.
How this applies: Exact primidone label supports ingredient-specific boundaries rather than inference solely from phenobarbital metabolism.
Does not quantify botanical interactions or make parent and metabolite concentrations equivalent. Maternal vitamin K guidance differs from evidence reviews. No universal supplement spacing.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Exact current available claims reviewed against captured originals; no clinical review asserted. | |
| Research summary published |
Article revision: 3d445c38ae3dbff8
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.