{"entity":{"id":"st-johns-wort-interaction","kind":"technology","name":"St John's wort: an interaction to avoid","aka":[],"tldr":"St John's wort is a herbal antidepressant whose active ingredient hyperforin switches on the liver enzyme CYP3A4 and the P-glycoprotein pump, cutting blood levels of irinotecan's active metabolite by 42% and imatinib by about a third. It is contraindicated with most tyrosine kinase, CDK4/6 and PARP inhibitors, and its effect lasts two weeks after stopping.","summary":"Hypericum perforatum induces CYP3A4 and P-glycoprotein through the pregnane X receptor. In a crossover pharmacokinetic study of five patients (Mathijssen et al., JNCI 2002), St John's wort reduced plasma levels of SN-38, the active metabolite of irinotecan, by 42 percent, enough to reduce efficacy; it lowers imatinib exposure by about a third and is contraindicated with most tyrosine kinase inhibitors, CDK4/6 inhibitors, PARP inhibitors, antiemetics such as aprepitant, and many antidepressants (serotonin syndrome). Its effect persists for two weeks after stopping. Depression in cancer patients should be treated with evidence-based psychotherapy or antidepressants chosen for their interaction profile. St John's wort is the clearest example of why oncology teams must ask about supplements at every visit.","status":"established","asOf":"2026-09-10","wikipedia":"https://en.wikipedia.org/wiki/Hypericum_perforatum","links":[{"label":"Effects of St. John's wort on irinotecan metabolism (JNCI 2002)","url":"https://doi.org/10.1093/jnci/94.16.1247"},{"label":"MSK About Herbs: St. John's wort","url":"https://www.mskcc.org/cancer-care/integrative-medicine/herbs/st-johns-wort"}],"tags":["complementary","supportive-care","evidence:harm"],"related":["idea-moon-supplement-interaction-database"],"cancers":[],"sections":["supportive-care"],"technologies":["dietary-supplements-treatment-interactions","integrative-oncology","psycho-oncology"],"targets":[],"drugs":["irinotecan","imatinib","folfiri","palbociclib","olaparib"],"companies":[],"institutions":["mskcc"],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":["b-toxicity-qol","b-misinformation"],"keyPapers":["paper-mathijssen-j-natl-cancer-inst"],"journals":[],"dependsOn":[],"notes":[],"principle":"Hyperforin activates PXR, increasing transcription of CYP3A4 and ABCB1, which accelerates clearance of drugs that are substrates of these systems.","strengths":["Interaction is well characterised and avoidable","Prompts systematic supplement reconciliation"],"limitations":["Halves exposure to irinotecan and many oral anticancer drugs","Effect lasts two weeks after stopping","Serotonin syndrome with antidepressants"]},"route":"/technologies/st-johns-wort-interaction/","neighbours":{"idea":[{"id":"idea-moon-supplement-interaction-database","kind":"idea","name":"An open supplement-drug interaction checker built into oncology prescribing","route":"/ideas/idea-moon-supplement-interaction-database/"}],"section":[{"id":"supportive-care","kind":"section","name":"Supportive Care & Survivorship","route":"/fronts/supportive-care/"}],"technology":[{"id":"dietary-supplements-treatment-interactions","kind":"technology","name":"Dietary supplements during cancer treatment: interactions and harms","route":"/technologies/dietary-supplements-treatment-interactions/"},{"id":"integrative-oncology","kind":"technology","name":"Evidence-based integrative oncology","route":"/technologies/integrative-oncology/"},{"id":"psycho-oncology","kind":"technology","name":"Psycho-oncology and distress screening","route":"/technologies/psycho-oncology/"}],"drug":[{"id":"folfiri","kind":"drug","name":"FOLFIRI (5-FU, leucovorin, irinotecan)","route":"/drugs/folfiri/"},{"id":"imatinib","kind":"drug","name":"Imatinib","route":"/drugs/imatinib/"},{"id":"irinotecan","kind":"drug","name":"Irinotecan (and liposomal irinotecan)","route":"/drugs/irinotecan/"},{"id":"olaparib","kind":"drug","name":"Olaparib","route":"/drugs/olaparib/"},{"id":"palbociclib","kind":"drug","name":"Palbociclib","route":"/drugs/palbociclib/"}],"institution":[{"id":"mskcc","kind":"institution","name":"Memorial Sloan Kettering Cancer Center","route":"/institutions/mskcc/"}],"bottleneck":[{"id":"b-misinformation","kind":"bottleneck","name":"Misinformation and unproven therapies","route":"/bottlenecks/b-misinformation/"},{"id":"b-toxicity-qol","kind":"bottleneck","name":"Toxicity and quality of life are undervalued","route":"/bottlenecks/b-toxicity-qol/"}],"paper":[{"id":"paper-mathijssen-j-natl-cancer-inst","kind":"paper","name":"Effects of St. John's wort on irinotecan metabolism","route":"/key-papers/paper-mathijssen-j-natl-cancer-inst/"}]}}