enzyme induction
8 interactions related to enzyme induction
digoxin + st. john's wort
St. John's wort revs up a gut transporter that digoxin depends on for absorption, so combining them quietly drains digoxin from the bloodstream. Because digoxin has so little room to spare, that drop can leave the drug too weak to control your heart.
verapamil + st. john's wort
St. John's wort is a potent inducer of intestinal CYP3A4 and P-glycoprotein, the same enzymes that break down verapamil before it reaches the bloodstream. Taking the two together sharply lowers verapamil's systemic exposure and can erase its therapeutic effect on blood pressure, heart rhythm, or migraine prevention.
phenytoin + st. john's wort
St. John's Wort activates the pregnane X receptor and induces drug-metabolizing enzymes (CYP3A4, CYP2C9, CYP2C19) and P-glycoprotein. Because phenytoin is cleared mainly by CYP2C9 and CYP2C19, taking St. John's Wort alongside it could speed phenytoin's breakdown and lower its blood levels, raising the theoretical risk of breakthrough seizures. Direct human data for phenytoin specifically are limited, so regulators treat this as a mechanism-based precaution rather than a documented loss of control.
phenytoin + ginkgo
Ginkgo biloba can induce CYP2C19, an enzyme involved in clearing phenytoin, which may lower phenytoin blood levels and raise the risk of breakthrough seizures. A published fatal case report described subtherapeutic phenytoin and valproate levels in a patient who had been self-administering ginkgo. Ginkgo also carries its own seizure-related signal. If you take phenytoin, avoid ginkgo and review any supplement changes with your doctor or pharmacist.
oxycodone + st. john's wort
St. John's Wort strongly induces CYP3A4, the main enzyme that clears oxycodone. In a controlled trial, taking St. John's Wort for about two weeks markedly lowered oxycodone blood levels and weakened its pain-relieving effect, so combining the two can leave pain poorly controlled.
phenytoin + folate
Phenytoin and folate interact in both directions: long-term phenytoin lowers folate through enzyme induction and reduced absorption, while supplemental folate can speed phenytoin clearance and lower its blood level enough to allow seizures to return in some people. The interaction is real but monitorable, so changes should be coordinated with your neurologist rather than avoided.
omeprazole + st. john's wort
St. John's wort induces the liver enzymes CYP3A4 and CYP2C19 that break down omeprazole. Taking the two together speeds up omeprazole clearance, lowers its blood levels, and can weaken its acid-suppressing effect — potentially undermining treatment of GERD, ulcers, or H. pylori eradication.
carbamazepine + st. john's wort
Both carbamazepine and St. John's Wort induce CYP3A4, the liver enzyme that primarily breaks carbamazepine down. The combined effect is hard to predict: carbamazepine already induces its own metabolism, so adding the herb may lower exposure most before that self-induction is fully established. The bigger danger comes at transitions — especially stopping St. John's Wort while still on carbamazepine, when the loss of enzyme induction can let carbamazepine levels climb toward toxicity.