herbal interaction
23 interactions related to herbal interaction
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.
warfarin + dong quai
Dong quai (Angelica sinensis) contains coumarin-family compounds (ferulic acid, osthole) and has antiplatelet activity in laboratory studies. A published case report described a previously stable warfarin patient whose INR climbed well above her target range within weeks of adding dong quai, then returned to normal after she stopped it. The signal rests on a single human case plus animal data, so it is taken seriously but is not extensively documented.
warfarin + danshen
Danshen (Salvia miltiorrhiza), widely used in traditional Chinese medicine for cardiovascular conditions, interacts with warfarin on two fronts. It slows warfarin's clearance (a pharmacokinetic effect that raises warfarin levels) and independently inhibits platelets and clotting (a pharmacodynamic effect). Published case reports describe severe over-anticoagulation and serious bleeds, including bleeding into the chest cavity, when patients added danshen to warfarin.
warfarin + feverfew
Feverfew (Tanacetum parthenium) inhibits platelet aggregation in laboratory studies via its parthenolide sesquiterpene lactones, which creates a theoretical, additive bleeding concern alongside warfarin. The evidence is bench/in-vitro only: systematic reviews classify feverfew's anticoagulant signal as low-level laboratory evidence, and there are no published human case reports of bleeding when feverfew is combined with warfarin. The cautious, mechanism-based approach is to avoid concentrated feverfew supplements while on warfarin and to disclose use to the clinician managing anticoagulation.
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.
digoxin + hawthorn
Hawthorn (Crataegus) shares digoxin's cardiac target and can cross-react with the immunoassays used to monitor digoxin, so a serum level may read falsely high or low. Controlled testing shows little change in how much digoxin reaches the bloodstream, so the practical concerns are additive cardiac effects and confounded lab monitoring rather than altered absorption.
clonazepam + passionflower
Clonazepam is a benzodiazepine that calms the brain by enhancing GABA, its main inhibitory neurotransmitter. Passionflower appears to act on the same GABA system and may increase the sedative effect of benzodiazepines. Taken together, the most likely result is additive drowsiness. The human evidence is limited and mostly suggestive, so this is best treated as a caution rather than a proven hazard.
alprazolam + kava
Kava's active compounds (kavalactones) act on the brain's GABA-A receptor, the same inhibitory system that alprazolam, a benzodiazepine, enhances. Taken together they cause additive central nervous system depression. A published case report describes a previously healthy 54-year-old man who became semi-comatose after three days of combining kava with his prescribed alprazolam, recovering once the kava was stopped. Kava also carries an independently documented risk of liver injury.
warfarin + ginger
Ginger has a mild antiplatelet effect that can add to warfarin's anticoagulant effect. Case reports describe a rise in INR after a person on stable warfarin started a daily ginger supplement, with the INR returning to range once the supplement was stopped. Ginger used in cooking and the occasional ginger tea is a food-level exposure and is generally considered safe.
tramadol + st. john's wort
Tramadol inhibits serotonin and norepinephrine reuptake, and St. John's Wort increases central serotonergic activity, so combining them can add together and raise the risk of serotonin syndrome. St. John's Wort also induces CYP3A4 and CYP2B6, enzymes involved in tramadol metabolism, which may lower levels of tramadol's active M1 metabolite and weaken pain relief.
prednisone + licorice
Glycyrrhizin in real licorice inhibits the enzyme 11-beta-hydroxysteroid dehydrogenase type 2, which normally inactivates cortisol and prednisolone at the kidney's mineralocorticoid receptor. Blocking it produces a pseudohyperaldosteronism state — sodium and water retention, rising blood pressure, and potassium loss. Layered onto prednisone, this can drive clinically significant hypokalemia, and severe cases of hypokalemic paralysis, arrhythmia, and refractory hypertension have been reported.
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.
warfarin + turmeric
Curcumin, the main active in turmeric, has antiplatelet activity that can add to warfarin's effect and raise bleeding risk. New Zealand's medicines regulator, Medsafe, issued an alert in 2018 after a patient stable on warfarin had their INR climb to a dangerously high level within weeks of starting a turmeric/curcumin product. A possible effect on the enzyme that clears warfarin has been seen only in animal and laboratory studies, not in people.
oral contraceptives + st. john's wort
St. John's Wort induces CYP3A4 and P-glycoprotein, increasing the clearance of contraceptive hormones and reducing the effectiveness of hormonal contraceptives.
ketoconazole + st. john's wort
St. John's Wort induces CYP3A4 and P-glycoprotein through PXR activation. Because oral ketoconazole is cleared by CYP3A4, regular St. John's Wort use can speed its breakdown, lower antifungal blood levels, and risk reduced effectiveness. The effect is established by mechanism and by analogy with other azole antifungals; topical ketoconazole is not a practical concern.
estrogen + dong quai
Dong quai (Angelica sinensis) shows estrogen-agonist activity in laboratory studies and can stimulate the growth of estrogen receptor-positive breast cancer cells in cell and animal models. Taken alongside prescribed estrogen, it adds an extra, unmeasured estrogenic signal in hormone-sensitive tissues. Dong quai also contains coumarin compounds that can add to bleeding risk, with one case report describing potentiation of warfarin.
amitriptyline + st. john's wort
St. John's wort induces the cytochrome P450 enzymes (and the P-glycoprotein transporter) that clear amitriptyline, measurably lowering amitriptyline blood levels and reducing its antidepressant and pain-relieving effect. Because both also raise serotonin signaling, combining them adds a theoretical risk of serotonin syndrome. The net effect can be a weaker antidepressant plus an added safety concern.
ibuprofen + ginkgo
Ibuprofen reduces platelet aggregation through COX-1 inhibition, and Ginkgo biloba has antiplatelet activity through ginkgolide B's antagonism of platelet-activating factor. Used together they can compound the effect on platelets and raise bleeding risk; a fatal intracerebral hemorrhage has been reported in a long-term ginkgo user who started regular ibuprofen.
bupropion + st. john's wort
St. John's wort induces drug-metabolizing enzymes that can lower bupropion blood levels and weaken its effect. A human case report also links the pair to a prolonged movement (dystonic) reaction from overlapping effects on brain chemicals. The often-cited additive seizure risk rests mainly on animal extract studies and is not well supported in people.
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.
nortriptyline + st. john's wort
St. John's wort induces the liver enzymes (chiefly CYP3A4, via the pregnane X receptor) that help clear nortriptyline, which can lower nortriptyline blood levels and weaken its antidepressant effect. The herb also adds serotonergic activity, which gives an additive, theoretical increase in the risk of serotonin syndrome.
digoxin + licorice
Glycyrrhizin in licorice inhibits the kidney enzyme 11-beta-hydroxysteroid dehydrogenase type 2, producing a state of apparent mineralocorticoid excess that causes sodium retention and potassium loss. The resulting low potassium makes the heart more sensitive to digoxin and can trigger toxic arrhythmias even when serum digoxin levels look normal.
warfarin + garlic
Concentrated garlic supplements may add to warfarin's blood-thinning effect, mainly through a mild antiplatelet action, though the clinical evidence for important bleeding is weak.