Many herbal supplements and can adversely impact the intended results of your prescription medications. Below we have listed many of these possible interactions. This list, however, is not a complete listing of all possible interactions, so we recommend that you still consult with your doctor before starting or altering your medications or herbal supplements.
| Drug Category | Herbs | Herb Effect | Mechanism (Evidence Type) |
| Alkaloids | High tannin-containing (e.g. caffeine-containing herbs, cat’s claw, tea, uva ursi) | Decreased plasma levels | Precipitation of alkaloids by tannins (UT) |
| Anesthetics | Kava, valerian | Prolongation of sedation time | Additive effect (CR) |
| Antihypertensives | a. Licorice b. Sympathomimetic herbs (e.g. ephedra) |
Decreased therapeutic effect | a. Increased salt and water retention (CR) b. Opposition of therapeutic action (P) |
| Antiarrhythmics | Cathartic laxatives (e.g. aloe, cascara, senna, yellow dock), diuretics (e.g. celery seed, corn silk, horsetail, juniper), licorice | Increased side effects (arrhythmia) | Increased potassium loss (P) |
| Antiarrhythmics | Anticholinergic herbs (not generally used clinically, e.g. belladonna) | Decreased therapeutic effect | Decreased absorbtion (P, TH) |
| Anticoagulants | Antiplatelet- aggregating (e.g., panax ginseng. feverfew, garlic, ginkgo) | Increased side effect (bleeding) | Inhibition of platelet aggregation through inhibition of thromboxane synthetase (ginger) (P); arachadonic acid production (feverfew) (P); inhibition of epinephrine induced in vitro (garlic) (P) platelet thromboxane synthetase aggregation (garlic) (P.CR); inhibition of platelet activating factor (ginkgo) (CR) |
| Anticoagulants: Warfarin |
Panax ginseng, St. John’s Wort | Opposition of therapeutic effect; decrease enzyne bioavailability | Unknown (CR); hepatic induction (CS) |
| Anticoagulants: Warfarin |
Coumarin-rich herbs (e.g., sweet clover, danshen), white clover | Increased therapeutic effect | Only danshen has been observed to do this clinically. Increased maximum concentration and decreased volume of distribution (CR, P) |
| Anticoagulants: Warfarin |
Vitamin K-rich herbs (e.g., collard, kale, spinach) | Decreased therapeutic effect | Opposes activity (CR, P) |
| Anticonvulsants | a. GLA- rich herbs b. Thujone -containing herbs (e.g., ceder, tansy, sage) |
Decreased therapeutic effect | GLA (CR) and thujone may decrease seizure threshold mechanism unknown |
| Anticonvulsants | Salicylate-rich herbs (e.g., cramp bark, willow, wintergreen) | Increased therapeutic effect | Transient: unknown mechanism (CR) |
| Antoconvulsants: Phenytoin |
Shankapulshpi (Ayurvedic preparation with multiple herbs) | Opposition therapeutic action | Decreased effectiveness of drug; decreased drug levels (CR) |
| Antiplatelet- aggregating |
Antiplatelt-aggregating (e.g., Panaz ginseng, feverfew, garlic, ginkgo) | Increased side effect (bleeding) | Similar therapeutic action (P, CR) |
| Barbiturates | Valerian | Increased therapeutic effect; increased side effects | Shown to prolong bariturate-induced sleep (AS) |
| Benzodiazepines | St John’s wort, kava | Decreased therapeutic efficacy; may increase side effects; increased sedation | Herb binds to GABA receptor site (AS,P) |
| Cardiac glycosides | Cardiac glycoside- containing herbs (e.g., foxglove, lily of the valley) | a. Enhanced therapeutic effect b. Increased side effects (arrhythmia) |
Same active constituents (TH) |
| Cardiac glycosides | Cathartic laxative herbs (e.g., aloe, cascara, senna, yellow dock), licorice, diuretic herbs (e.g., celery seed, corn silk, horsetail, juniper) | Increased side effects (arrhythmia) | Increased potassium loss (TH) |
| Cardiac glycosides | Quinine-containing herb (e.g., cinchona bark) | Increased plasma levels | (TH) |
| Cholesterol- lowering drugs |
Garlic, artichoke, ginger, fenugreek | Increased therapeutic effect | Similar clinical effect via different mechanism (TH) |
| Corticosteroids | Cathartic laxative herbs (e.g., aloe, cascara, senna, yellow dock), diuretic herbs (e.g., celery seed, corn silk, horsetail, juniper) | Increased side effects | Both cause increased potassium loss (TH) |
| Corticosteroids | Licorice | Increased plasma levels | Increased half-life (increased bioavailability) (CR); inhibition of II-B-dehydrogenase (P) |
| Corticosteroids | Panax ginseng | Increased side effects | Similar side effects of CNS stimulation and insomnia (CR) |
| Digoxin | Siberian ginseng | Incraesed plasma level | Mechanism unknown: validated by rechallenge (CR) |
| Digoxin | a. Kyushin (Chinese remedy containing the venom of the Chinese toad) b. Panax ginseng |
Increased serum levels | Interferes with assay (P, CR) without toxic effects |
| Diuretic: Lasix | Panax ginseng | Decreased therapeutic effect | Diuretic resistance with ginseng; unknown mechanism (CR) |
| Diuretic: Potassium sparing | Licorice | Decreased therapeutic side effect | Interferes with potassium- sparing effects by wasting K- |
| Estrogen replacement therapy | a. Herbs high in phytoestrogens (e.g., soy,fenugreek, licorice, black cohosh) b. Panax ginseng |
a. Increased therapeutic effect to excess b. Increased side effect (estrogen excess) |
a. Never reported (TH) b. Reported in few cases to produce postmenopausal bleeding or mastalgia (CR) |
| General medication | High-fiber herbs (e.g., flax, psyllium, acacia, slippery elm, marshmallow) | Decreased absorption | (P) |
| General medication | “Hot” remedies (e.g., ginger, garlic, black pepper, red pepper) | Increased absorption | Taken internally, “hot” remedies lead to vasodilatation of gut wall and increased absorpotion (TU) |
| GI motility drugs | Anticholinergic herbs (not gennerally used clinically, e.g., belladonna) | Decreased activity | Opposition of therapeutic activity |
| Hepatotoxic drugs | Hepatotoxic herbs (e.g., borage, coltsfoot, comfrey, rue, tansy) | Increased side effect (hepatotoxicity) | Additive toxicity from similar side effects (CR) |
| Hypoglycemic agents: Oral and insulin | Hypoglycemic (e.g., Panax ginseng, garlic, fenugreek, bitter melon, aloe, gymnema) | Enhanced therapeutic effect | a. Direct hypoglycemic activity (CR, AS, P) b. Decreased glucose absorption |
| Hypoglycemic agents: Oral and insulin | Hypoglycemic (e.g., cocoa, rosemary, stinging nettle) | Decreased therapeutic effect | Direct opposition of therapeutic action (CS) |
| Immune suppressants | Echinacea, astragalus | Opposition of therapeutic action | General immune stimulation by these herbs may interfere with ability of immunosuppressive drugs to prevent tissue rejection: never reported (TH) |
| Iron | Tannin-rich herbs (e.g., caffine-containing herbs. cat’s claw, tea, uva ursi) | Decreased therapeutic effect | Tannin binds with iron, decreasing absorption (TH, P) |
| Lithium | Diuretic herbs (e.g., celery seed, corn silk, horsetail, juniper) | Increased side effects | Decreased sodium leads to increased lithium toxicity |
| Lower seizure thresholds (drugs that) | GLA- rich herbs (e.g., evening primrose, borage, black currant) | Increased side effect to additive side effect | Decreased seizure threshold (CR) |
| Methotrexate and similar cytotoxic drugs | Salicylate herbs (e.g., cramp bark, willow, wintergreen) | Increased plasma levels (toxicity) | Decreased excretion (TH) |
| Minerals | Fiber- containing herbs (e.g., flax, psyllium, acaia, slippery elm, marshmallow) | Decreased bioavailability | Psyllium has been reported to decrease the absorption of Ca, Mg, Cu, Zn (CR) |
| Monoamine oxidase inhibitors (MAOIs) | Panax ginseng, bioactive amines, licorice | Increased side effects | Additive side effects may lead to toxicity; glycyrrhizin is reported to be a very potent MAOI (TH, CR) |
| Monoamine oxidase inhibitors (MAOIs) | Ginkgo | Increased therapeutic effect; increased side effects | Inhibition of monoamine oxidase (P) |
| Nonsteroidal anti- inflammatory drugs (NSAIDs) | Gastric irritant herbs (e.g., caffeine, rue, uva ursi) | Increased side effects | Similar side effects may increase risk of gastric erosion and bleeding (TH) |
| Nonsteroidal anti- inflammatory drugs (NSAIDs) | Nettles | Increased therapeutic effect | Potentiation of the anti inflammatory activity of NSAIDs (CT) |
| Opioids | Panax ginseng | Decreased therapeutic effects | Animal model demonstrated the blunting of the analgesic effects of morphine via a non- opioid receptor- mediated mechanism (AS) |
| Photosensitizing drugs | Photosensitizing herbs (e.g., St. John’s wort. angelica, rue, fennel) | Increased side effetcs | Furanocournarins found often in umbrelliferae resemble pso- ralens (P, AS, CR) |
| Salicylates | Herbs that alkalinize urine (e.g., uva ursi) | Decreased plasma levels | Increased urinary excretion (P) |
| Sedative hypnotics | Opiaid herbs (e.g., opium poppy, California poppy) | Increased side effects (CNS depression) | Additive side effects |
