The short answer
St. John's wort must not be used with fosamprenavir under the cited prescribing guidance because it may lower active-drug levels, reduce HIV treatment response and contribute to resistance. Spacing doses is not a solution, and the interaction may persist after St. John's wort is stopped.
What this answer covers
Applies to oral fosamprenavir regimens; source labeling concerns fosamprenavir-calcium products, with additional guidance for fosamprenavir/ritonavir.
- Supplement or preparation
- St. John's wort
- Medication ingredient
- fosamprenavir
Evidence and practical considerations
Absorption & effectiveness
An exact current regulatory contraindication establishes the clinically actionable claim, but the missing direct pair study and unquantified magnitude justify supported-with-conditions rather than an unqualified evidence-strength claim.
- Exact scope
- St. John's wort (Hypericum perforatum) with fosamprenavir
- Medication form and route
- oral fosamprenavir exposure
- Timing or duration
- Risk applies during concomitant use and may persist after St. John's wort discontinuation because enzyme induction is not limited to same-time dosing.
What remains uncertain
- Direct fosamprenavir pair pharmacokinetic data were not found; the label warning relies on known enzyme induction and antiretroviral risk.
- The finding must not be generalized to every botanical.
- Dose separation is not a mitigation because the mechanism is sustained induction.
Factors that may matter: St. John's wort product potency and hyperforin content; duration of botanical use; fosamprenavir regimen with or without ritonavir; baseline viral suppression and resistance history.
Read the supporting source summaries
Source 1: current United States regulatory prescribing information
dailymed.nlm.nih.gov · Source check Jul 24, 2026
Population: Patients receiving labeled oral fosamprenavir-calcium products.
The label states decreased amprenavir with St. John's wort and contraindicates coadministration because it may cause loss of virologic response and possible resistance to fosamprenavir or the protease-inhibitor class.
No direct fosamprenavir-plus-St.-John's-wort human pharmacokinetic trial was identified; magnitude is not quantified.
Source 2: United States government patient drug record
clinicalinfo.hiv.gov · Source check Jul 24, 2026
Population: People prescribed fosamprenavir for HIV.
NIH identifies St. John's wort among products that should not be taken with fosamprenavir.
Patient guidance does not quantify pharmacokinetics.
Research assessment: · Open full citations ↗
Timing & monitoring
The current regulatory label explicitly contraindicates coadministration, and specialist HIV guidance corroborates avoidance. This is sufficient for a supported management requirement.
- Exact scope
- St. John's wort (Hypericum perforatum) with fosamprenavir
- Medication form and route
- oral fosamprenavir exposure
- Timing or duration
- Avoid throughout fosamprenavir therapy; induction may persist after stopping the botanical.
What remains uncertain
- No evidence supports a safe same-day separation interval.
- The exact duration of residual induction depends on product and exposure.
Factors that may matter: unknown St. John's wort potency; duration of prior botanical use; antiretroviral resistance risk.
Read the supporting source summaries
Source 1: current United States regulatory prescribing information
dailymed.nlm.nih.gov · Source check Jul 24, 2026
Population: Patients receiving fosamprenavir.
Coadministration with St. John's wort is contraindicated.
The label does not state a washout interval.
Source 2: specialist HIV interaction database
hiv-druginteractions.org · Source check Jul 24, 2026
Population: People receiving fosamprenavir-containing antiretroviral regimens.
The database states St. John's wort must not be used with fosamprenavir/ritonavir and notes that induction can persist after discontinuation.
Secondary specialist synthesis; direct pair data are limited.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Research summary published |
Article revision: d915e58088402155
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?
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Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.