herbal interaction
24 interactions related to herbal interaction
warfarin + dong quai
Dong quai (Angelica sinensis) contains coumarin derivatives (ferulic acid, osthole) and has documented antiplatelet activity. A widely cited case report (Page & Lawrence, Pharmacotherapy 1999, PMID 10417036) described a woman whose INR rose to 4.9 within four weeks of adding dong quai 565 mg once to twice daily to stable warfarin.
warfarin + danshen
Danshen (Salvia miltiorrhiza), widely used in traditional Chinese medicine for cardiovascular indications, has both pharmacokinetic (decreased clearance of R- and S-warfarin) and pharmacodynamic (antiplatelet, antithrombotic) interactions with warfarin. Multiple published case reports describe massive over-anticoagulation with INRs above 8 and serious bleeds including haemothorax.
warfarin + feverfew
Feverfew (Tanacetum parthenium) inhibits platelet aggregation in vitro via its parthenolide sesquiterpene lactones. There are no robust human case reports of bleeding with warfarin specifically, but standard herbal-interaction references (StatPearls, Australian Prescriber) recommend avoidance based on the pharmacologic plausibility of additive bleeding risk.
verapamil + st. john's wort
St. John's wort is a potent inducer of intestinal CYP3A4 and P-glycoprotein. In a controlled study, two weeks of St. John's wort reduced the AUC of R- and S-verapamil by roughly 78-80%, dramatically lowering systemic drug exposure and likely therapeutic effect.
digoxin + st. john's wort
St. John's wort induces intestinal P-glycoprotein, increasing efflux of digoxin and reducing its absorption. Controlled studies show digoxin AUC falls roughly 25% and peak concentrations around 30-36% after two weeks of St. John's wort, potentially producing therapeutic failure in rate control or heart failure management.
digoxin + hawthorn
Hawthorn (Crataegus) has digoxin-like positive inotropic activity, may modulate P-glycoprotein efflux, and can interfere with serum digoxin immunoassays. Concurrent use raises the risk of additive cardiac effects and erroneous digoxin level readings even though formal pharmacokinetic studies show little change in digoxin AUC.
clonazepam + passionflower
Passionflower contains constituents that bind GABA-A receptors and may enhance the binding activity of benzodiazepines at those receptors. Combined with clonazepam, the effect is additive central nervous system depression and increased sedation.
alprazolam + kava
Kava contains kavalactones that potentiate GABA-A receptor binding, producing additive CNS depression when combined with alprazolam, a benzodiazepine that also enhances GABA-A activity. A published case report describes a 54-year-old man who became semi-comatose after taking alprazolam with kava for three days.
warfarin + ginger
Ginger inhibits thromboxane synthase and reduces platelet aggregation; case reports describe elevated INR after addition of oral ginger to stable warfarin therapy. A 2019 case report (Rubin et al., Case Reports in Medicine) and the Tan 2021 BJCP systematic review document the signal, though controlled trials in healthy volunteers have been mixed.
tramadol + st. john's wort
Tramadol inhibits serotonin and norepinephrine reuptake, and St. John's Wort increases central serotonergic activity, so combining them raises the risk of serotonin syndrome. St. John's Wort also induces CYP3A4 and CYP2B6, which can reduce tramadol's active M1 metabolite and weaken analgesia.
prednisone + licorice
Glycyrrhizin in licorice inhibits the enzyme 11-beta-hydroxysteroid dehydrogenase type 2, prolonging the half-life of glucocorticoids and dramatically amplifying mineralocorticoid effects. The combination potentiates sodium retention, hypertension, and hypokalemia, and has been linked to severe hypokalemic crises.
oxycodone + st. john's wort
St. John's Wort strongly induces CYP3A4, the main enzyme that metabolizes oxycodone. In a controlled crossover trial, St. John's Wort cut oral oxycodone plasma exposure (AUC) by roughly 50% and significantly reduced its analgesic effect.
warfarin + turmeric
Curcumin, the main active in turmeric, has antiplatelet activity and may also inhibit CYP2C9 metabolism of warfarin, raising warfarin levels. New Zealand Medsafe issued an alert in 2018 after a patient's INR rose above 10 within weeks of starting a turmeric/curcumin product on previously stable warfarin therapy.
oral contraceptives + st. john's wort
St. John's Wort induces CYP3A4 and P-glycoprotein, which accelerates the metabolism of ethinyl estradiol and progestins in combined oral contraceptives. Clinical trials have documented breakthrough bleeding and reduced contraceptive hormone exposure when the two are combined, raising the risk of ovulation and unintended pregnancy.
ketoconazole + st. john's wort
St. John's Wort is a potent inducer of CYP3A4 and P-glycoprotein via PXR activation, which can accelerate the metabolism of ketoconazole and reduce its antifungal blood concentrations and clinical effectiveness.
estrogen + dong quai
Dong quai (Angelica sinensis) shows estrogen-agonist activity in vitro and promotes growth of estrogen receptor-positive breast cancer cells. Combining it with prescribed estrogen therapy may add unwanted estrogenic stimulation, and dong quai's coumarin content increases bleeding risk in patients also on hormone therapy with VTE risk.
amitriptyline + st. john's wort
St. John's wort induces CYP3A4 and CYP2D6 enzymes that metabolize amitriptyline, reducing its plasma concentrations by up to 22%, while simultaneously adding serotonergic activity that can trigger serotonin syndrome. The combined result is paradoxical: less antidepressant effect plus higher risk of a potentially fatal serotonin reaction.
ibuprofen + ginkgo
Ibuprofen inhibits platelet aggregation through COX-1, and Ginkgo biloba inhibits platelet-activating factor through ginkgolide B. Combining them increases the risk of bleeding, with case reports of fatal intracerebral hemorrhage.
bupropion + st. john's wort
Bupropion lowers the seizure threshold and St. John's wort may compound that risk, and the herb's induction of CYP enzymes (particularly the role of CYP2B6 and downstream pathways) can also alter bupropion exposure. Both also influence monoamine signaling, raising the risk of additive CNS effects.
omeprazole + st. john's wort
St. John's wort potently induces CYP3A4 and CYP2C19, the enzymes responsible for omeprazole metabolism. Co-administration significantly lowers omeprazole plasma concentrations, reducing its acid-suppressing efficacy and potentially compromising treatment of GERD, ulcers, or H. pylori eradication.
raloxifene + st. john's wort
Although raloxifene is cleared primarily by glucuronidation rather than CYP3A4, St. John's Wort induces P-glycoprotein and other transporters that may reduce raloxifene exposure. Drug interaction databases list a documented reduction in raloxifene serum concentration with concurrent use, potentially undermining osteoporosis treatment.
nortriptyline + st. john's wort
St. John's wort induces CYP3A4 and CYP2D6, the enzymes responsible for metabolizing nortriptyline, reducing nortriptyline blood levels and antidepressant effect. The herb also adds serotonergic activity that may increase risk of serotonin syndrome.
digoxin + licorice
Glycyrrhizin in licorice inhibits 11-beta-hydroxysteroid dehydrogenase type 2, mimicking aldosterone excess and causing sodium retention and potassium wasting. The resulting hypokalemia sensitizes the myocardium to digoxin and can trigger toxicity (arrhythmias, heart block) even at therapeutic serum digoxin levels.
warfarin + garlic
Concentrated garlic supplements have antiplatelet activity (mainly via ajoene and allicin) and have been associated with elevated INR and bleeding when added to warfarin in case reports and herbal-interaction reviews. The Vaes & Chyka review in Annals of Pharmacotherapy classified garlic as a potential potentiator of warfarin via additive antithrombotic effect.