cyp2c19
8 interactions related to cyp2c19
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.
propranolol + st. john's wort
St. John's Wort induces several liver drug-metabolizing enzymes, including CYP1A2 and CYP3A4, plus the transporter P-glycoprotein. Propranolol is cleared mainly through CYP1A2 and CYP2D6, so regular St. John's Wort use can plausibly speed up its breakdown and weaken its effect. Direct studies of this specific pair are lacking; the concern is based on St. John's Wort's confirmed enzyme-inducing action, its documented lowering of theophylline (which shares propranolol's CYP1A2 pathway), and a case report of lost intraocular-pressure control in a glaucoma patient on a topical beta-blocker.
cbd + sertraline
CBD inhibits CYP2C19, one of several enzymes that help break down sertraline, so adding CBD can raise sertraline exposure. A single published case report describes low sodium (hyponatremia) and cognitive decline in an older intermediate-metabolizer patient who added over-the-counter CBD to long-standing sertraline. The evidence is limited to this one report, so treat it as a reason for caution and prescriber discussion rather than a strong contraindication.
cannabis + ssris
Cannabinoids inhibit liver enzymes (including CYP2C19) that clear several SSRIs such as sertraline, citalopram, and escitalopram, which can raise SSRI plasma levels. Cannabinoids also touch the serotonin system, and case reports describe serotonin syndrome precipitated by high-potency cannabis in patients on serotonergic regimens.
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.
escitalopram + st. john's wort
Escitalopram is a selective SSRI cleared mainly by CYP2C19 and CYP3A4. St. John's wort independently raises serotonin tone and is a strong inducer of those same enzymes and P-glycoprotein. Taken together, the combination can add to serotonergic effects and, through enzyme induction, lower escitalopram levels and blunt its antidepressant effect. Documented serotonin syndrome cases with St. John's wort involve other SSRIs rather than escitalopram specifically, so the combination is best avoided rather than treated as a guaranteed emergency.
cbd + clobazam
CBD inhibits CYP2C19, the enzyme that clears N-desmethylclobazam, the active metabolite of clobazam. Taking the two together raises N-desmethylclobazam levels substantially, increasing sedation, drowsiness, drooling, and unsteadiness. This interaction is documented in the FDA-approved Epidiolex prescribing information and in clinical studies in children with epilepsy.