St John's wort reduces oral contraceptive effectiveness and has caused breakthrough bleeding and unintended pregnancies.
What's happening
Hyperforin, a primary constituent of St John's wort, activates the pregnane X receptor (PXR) and induces cytochrome P450 3A4 and P-glycoprotein. CYP3A4 metabolizes ethinylestradiol and most progestins; inducing it accelerates contraceptive clearance and lowers circulating hormone levels. A direct RCT (Pfrunder 2003, N=17 healthy women on a low-dose combined OC) found breakthrough bleeding rose from 6/17 (35%) on OC alone to 13/17 (77%, p<0.015) with SJW 300 mg twice daily and 15/17 (88%, p<0.001) with SJW 300 mg three times daily — a clean dose-response pattern. Ovulation was not detected but follicle-like structures appeared sporadically, meaning the contraceptive margin narrows. Pharmacovigilance confirms the clinical impact: by December 2001 the UK and Sweden together had received 9 reports of unintended pregnancies attributed to SJW + OC co-use, all in women who had used OCs without problems for at least seven months before adding SJW. Products with greater than 1 mg hyperforin/day are considered high-risk; a low-hyperforin extract study (Will-Shahab 2009) showed no measurable PK interaction, but most retail SJW products are high-hyperforin and hyperforin content is rarely disclosed on US labels. CYP3A4 induction persists for 1-2 weeks after stopping SJW. Progestin-only pills, patches, rings, implants, hormonal IUDs, and levonorgestrel emergency contraception are all metabolized by CYP3A4 and likely affected; direct trial data on non-combined methods are sparse.
Recommendation
If you rely on oral contraception, do not take St John's wort without discussing it with your prescriber. If you are taking both, use a reliable backup method (condom, non-hormonal IUD, abstinence) during SJW use and for at least two weeks after stopping. Breakthrough bleeding on a previously stable OC regimen is a warning sign. For levonorgestrel emergency contraception, SJW use in the prior 1-2 weeks reduces efficacy — a copper IUD is a more reliable alternative.
Timing
Spacing doses does not help. CYP3A4 induction is a transcriptional effect developing over days and resolving over days — unrelated to hour-by-hour timing.
Sources
— PMID:12911359 — Pfrunder A et al. Interaction of St John's wort with low-dose oral contraceptive therapy: a randomized controlled trial. Br J Clin Pharmacol 2003.
— PMID:17486092 — Borrelli F, Izzo AA. St John's wort (Hypericum perforatum): drug interactions and clinical outcomes. CNS Drugs 2007.
— PMID:31943241 — Nicolussi S et al. Clinical relevance of St John's wort drug interactions revisited. Br J Pharmacol 2020.
— https://pmc.ncbi.nlm.nih.gov/articles/PMC11283811/ — Co-administration of St John's wort and hormonal contraceptives: a systematic review. 2024.
How it works
Hyperforin, a primary constituent of St John's wort, activates the pregnane X receptor (PXR) and induces cytochrome P450 3A4 and P-glycoprotein. CYP3A4 metabolizes ethinylestradiol and most progestins; inducing it accelerates contraceptive clearance and lowers circulating hormone levels. P-glycoprotein induction additionally reduces intestinal absorption. Net effect: less hormone in circulation, less ovulation suppression, more breakthrough bleeding and pregnancy risk.
Who should be careful
Women on combined oral contraceptives — highest evidence base.
Women on progestin-only pills, patches, rings, implants, hormonal IUDs — same mechanism, sparser direct data.
Women on combination patches or rings — same caution as combined OCs.
Anyone needing levonorgestrel emergency contraception — SJW use in the prior 1-2 weeks reduces efficacy.
What we don't know
Post-stopping-SJW washout time is not precisely quantified (CYP3A4 induction typically persists 1-2 weeks). Direct RCTs on progestin-only pills, hormonal IUDs, or emergency contraception + SJW are lacking.
Why this severity
DANGER. Unintended pregnancy is definitionally non-reversible. The interaction is RCT-confirmed (Pfrunder 2003, dose-response p<0.001), mechanistically explained, and validated by pharmacovigilance (9 documented unintended pregnancies by 2001).
Evidence quality (GRADE): high
Frequently Asked Questions
Can I take birth control and st johns wort together?
St John's wort reduces oral contraceptive effectiveness and has caused breakthrough bleeding and unintended pregnancies.. If you rely on oral contraception, do not take St John's wort without discussing it with your prescriber. If you are taking both, use a reliable backup method (condom, non-hormonal IUD, abstinence) during SJW use and for at least two weeks after stopping. Breakthrough bleeding on a previously stable OC regimen is a warning sign. For levonorgestrel emergency contraception, SJW use in the prior 1-2 weeks reduces efficacy — a copper IUD is a more reliable alternative.
How should I time birth control and st johns wort?
Spacing doses does not help. CYP3A4 induction is a transcriptional effect developing over days and resolving over days — unrelated to hour-by-hour timing.
Is this interaction dangerous?
This interaction is rated “Danger” by Formulate. Hyperforin, a primary constituent of St John's wort, activates the pregnane X receptor (PXR) and induces cytochrome P450 3A4 and P-glycoprotein. CYP3A4 metabolizes ethinylestradiol and most progestins; inducing it accelerates contraceptive clearance and lowers circulating hormone levels. A direct RCT (Pfrunder 2003, N=17 healthy women on a low-dose combined OC) found breakthrough bleeding rose from 6/17 (35%) on OC alone to 13/17 (77%, p<0.015) with SJW 300 mg twice daily and 15/17 (88%, p<0.001) with SJW 300 mg three times daily — a clean dose-response pattern. Ovulation was not detected but follicle-like structures appeared sporadically, meaning the contraceptive margin narrows. Pharmacovigilance confirms the clinical impact: by December 2001 the UK and Sweden together had received 9 reports of unintended pregnancies attributed to SJW + OC co-use, all in women who had used OCs without problems for at least seven months before adding SJW. Products with greater than 1 mg hyperforin/day are considered high-risk; a low-hyperforin extract study (Will-Shahab 2009) showed no measurable PK interaction, but most retail SJW products are high-hyperforin and hyperforin content is rarely disclosed on US labels. CYP3A4 induction persists for 1-2 weeks after stopping SJW. Progestin-only pills, patches, rings, implants, hormonal IUDs, and levonorgestrel emergency contraception are all metabolized by CYP3A4 and likely affected; direct trial data on non-combined methods are sparse.
The free checker lets you add any combination of supplements and medications at once. The free web app goes further — every stack change surfaces interaction alerts automatically.