Herbs with Drug Interactions - a Partial List

By popular request, here is a partial list of herbs with drug interactions.  It is by no means complete!  If you are taking medications, please check with your prescribing physician before taking any supplements.

Herb - alphabetical by common name Possible Drug Interaction Possible Contraindications
Ashwaganda Withania somnifera None known. (PPP, 601) May potentiate the effects of barbituates (Atal and Schwarting). (BSH, 124) High dosages of alkaloids from Withania exhibit prolonged hypotensive, bradycardiac and respiratory stimulant actions, may also have depressant effect on higher cerebral centres; sedative effects have also been demonstrated. (CAACH, 138)
Bilberry Vaccinium myrtillus None known. (HM, 18; TGHM, 88) Possible interaction with warfarin and antiplatelet drugs in very high doses. (PPP, 301)  Very high doses should be used cautiously in patients with haemorrhagic disorders and in those taking warfarin or antiplatelet drugs. (PPP, 301)
Bladderwrack Fucus vesiculosus None known. (HM, 213) Caution indicated within iodine-containing drugs. (AEHD, 44)  Therapeutic use is not recommended in hyperthyroidism, long-term therapeutic use is not recommended. (BSH, 54) Contraindicated in hyperthyroidism, cardiac problems. (BHC, 38) In rare cases allergic reactions involving serious overall reactions may occur. (TGHM, 315)
Black Cohosh Cimicifuga racemosa Drugs for iron therapy Inhibits iron absorption
Bugleweed Lycopus virginicus
 None known. (TGHM, 99) Do not take with thyroid medications. (BSH, TGHM, 99) Contraindicated in thyroid hypofunction, enlargement of the thyroid without functional disorders. (TGHM, 99; BSH, 72) Administration of the herb interferes with diagnostic procedures using radioactive isotopes. (TGHM, 99)
Bupleurum Bupleurum falcatum
The use of alcohol, sedatives and other central nervous system depressants, in conjunction with this herb, may cause synergistic sedative effects. (WHO, 73) Bupleurum has a slight sedative effect in some patients and may also increase bowel movements and flatulence (wind). (CAACH, 23; WHO, 73, 74; PPP, 317) May cause nausea and reflux in sensitive patients. (PPP, 317) 
Californian Poppy
Eschscholtzia californica
 May potentiate pharmaceutical MAO-inhibitors. (BSH, 49) This herb should be restricted in its application to experienced and well-trained practitioners. (PPP, 232) There is a theoretically increased risk of neurotoxicity and other adverse effects (although no known incidence). (PPP, 233) The following cases should be approached with caution: (1) concurrent prescription of powerful analgesics, (2) pain in children, (3) neurological disease, (4) depression and psychosis, (5) liver and kidney disease, and (6) history of allergic or anaphylactic reactions. (PPP, 232)
Cascara sagrada Rhamnus purshiana Most intestinally absorbed drugs; Thiazide-type diuretics Interferes with absorption of the pharmaceutical agent; Raise blood pressure or deplete potassium
Chamomile Matricaria recutita Drugs for iron therapy Inhibits iron absorption
Coleus Coleus forskohlii Forskolin has the ability to potentiate many drugs. Use cautiously in patients taking prescribed medication. (CAACH, 106) Contraindicated in hypotension. (CAACH, 106) 
Dong Quai Angelica sinensis  Based on animal studies, caution is advised for patients receiving chronic treatment with anticoagulant drugs such as Coumadin (warfarin). (PPP, 352) Containdicated in bleeding or very heavy menstruation, first trimester of pregnancy, acute viral infections such as colds or influenza. (CAACH, 5-6; BSH, 11; PPP, 352) Also contraindicated in diarrhea caused by weak digestion and in haemorrhagic disease. (PPP, 352) Cardiovascular side effects include excessive bleeding. (TCPHP, 290) Dong quai has two furanocoumarins (psoralen and bergapten), which are photoreactive and have the potential to cause severe photodermatitis. These furanocoumarins are also photocarcinogenic. However, the risk of phototoxicity in humans from ingestion of Dong quai has not been characterized. (TCPHP, 290-291) 
Echinacea Echinacea purpurea  None known. (HM, 97; TGHM, 123; WHO, 142; PPP, 360) Commission E cautioned that the herb should not be used in systemic diseases such as tuberculosis, leukosis, collagenosis, multiple sclerosis, AIDS, HIV infections, and other autoimmune diseases (based on theoretical considerations and not on any reports of adverse findings). (HM, 97; TGHM, 123; WHO, 141-142; PPP, 359) Caution is advised for transplant patients taking immunosuppressive drugs; short-term therapy is suggested. (PPP, 360) Should not be administered to patients with known allergy to any plant of Asteraceae (Compositae). (WHO, 142; PPP, 359; HM, 97) Allergic concern based upon case reports. (TCPHP, 301; PPP, 359; WHO, 142)
Evening Primrose Oil Oenothera biennis Anticonvulsants and tricyclic antidepressants Lowers the seizure threshold, thus increasing drug dosage requirements
Feverfew Tanacetum parthenium Drugs for iron therapy; Warfarin sodium, heparin, aspirin and other anticoagulants Inhibits iron absorption; Augments the anticoagulant effect, thus altering clotting or bleeding times
Garlic Allium sativum
Contains glucose. Use with caution in patients taking anti-platelet drugs. Garlicís antiplatelet effect might be dangerous in patients taking warfarin or antiplatelet agents such as aspirin, ticlopidine, clopidogrel, or dipyrida-mole. (TCPHP, 118; HM, 115; WHO, 25)  Contraindication with gastrointestinal disturbance; in rare instances, there may be changes to the flora of the intestine, or allergic reactions. (TGHM, 134; HM, 145; BSH, 6; BHC,106) May also cause heartburn, nausea, vomiting, and diarrhea if taken on an empty stomach. (WHO, 26) HM suggests that substantial amounts of garlic should not be consumed prior to surgery. (HM, 145) May increase the risk of postoperative bleeding. (WHO, 25; ESCOPM, 2; AEHD, 229) Allergic and dermatologic concern based upon case reports. (AEHD, 229; WHO, 26; TCPHP, 116-117, 301) Hematologic concern based upon in vitro data and case reports. (TCPHP, 301) 
Ginger Zingiber officinale Contraindicated with gallstones; consult a physician first. (HM, 156; BSH, 125; TGHM, 136) May increase the chance of bleeding. (PPP, 401) Overdose may lead to a blood-thinning effect and an increase in gastric secretory activity leading to heartburn. (PPP, 401; ESCOPM, 1996, 1) Topical application may cause contact dermatitis in sensitive patients. (PPP, 401); Warfarin sodium, heparin, aspirin and other anticoagulants None known. (HM, 156, TGHM, 136) Caution should be used in patients taking anticoagulants and antiplatelet drugs because of its potential antiplatelet effect. (TCPHP, 129; CAACH, 106) May increase the absorption of pharmaceutical drugs. (PPP, 401) Caution indicated with patients taking blood-thinning drugs such as warfarin, or aspirin or who have increased risk of haemorrhage. (PPP, 401) May enhance absorption of sulphaguanidine. (ESCOPM, 1); Augments the anticoagulant effect, thus altering clotting or bleeding times
Ginko Ginko biloba Warfarin sodium, heparin, aspirin and other anticoagulants Augments the anticoagulant effect, thus altering clotting or bleeding times
Ginseng and other herbs that contain cardiac glycosides Insulin and related drugs for diabetes mellitus; Digoxin; Warfarin soldium, heparin, aspirin and other anticoagulants Affects glucose levels; compromises dosage potency; alters bleeding or clotting times
Golden Seal Hydrastis canadensis  Berberine, an alkaloid constituent of this herb, may reinforce the effects of other drugs which displace the protein binding of bilirubin. (PPP, 295) Contraindicated in hypertensive conditions. (PPP, 294) Fresh plant may cause irritation to the mucosa. (BSH, 62) Canadian regulations do not allow golden seal as a non-medicinal ingredient for oral use products. (BSH, 62)
Hawthorn Crataegus monogyna 
digitalis glycosides, beta-blockers and other hypotensive drugs  May potentate the actions of digitalis, though this action has not been confirmed. (HM, 186-188) Hawthorn may act in synergy with digitalis glycosides, beta-blockers and other hypotensive drugs. Modification of drug dosage may be required. (PPP, 446) Drug interactions are also theoretically possible with cardioactive medications. (TCPHP, 257)
Kava Kava Piper methysticum Potentiation of effectiveness is possible for substances on the central nervous system, such as alcohol, barbituates and psychopharmacological agents. (TGHM, 156; PPP, 462) Caution indicated with medications for insomnia or anxiety such as benzodiazepine. (PPP, 463; TCPHP, 33) There is a risk of sudden abnormal movements (a dystonic reaction) when combined with antipsychotic drugs. (TCPHP, 37) May reduce the efficacy of Levodopa, a medication for Parkinsonís disease; may interact with antiplatelet drugs or anticoagulants (e.g., warfarin, heparin) however there are no case reports of such interactions. (TCPHP, 36) Extended use can cause discoloration of the skin, nails, and hair. (TGHM, 156; PPP, 462) In rare cases, contact type dermatitis can occur. (PPP, 462) Also accommodative disturbances, such as enlargement of the pupils and disturbances of the oculomotor equilibrium, have been reported. (TGHM, 156; TCPHP, 35) Contraindicated in endogenous depression. (HM, 223) Chronic usage may result in skin rash, shortness of breath, liver damage and neurological manifestations may occur. (PPP, 463) dermatologic and neurologic concern based upon case reports. (TCPHP, 301) Do not exceed recommended dose. (BSH, 86) 
Korean Ginseng Panax ginseng  May interact with monoamine oxidase inhibitor phenelzine and also with warfarin. (PPP, 429; WHO, 176). Do not use with stimulants, including excessive use of caffeine. (HM, 174, PPP, 429) Contraindicated for hypertension. (BSH, 81; HM, 174) Contraindicated with signs of heat, acute infections, acute asthma, hypertension, excessive menstruation or nose bleeds. (PPP, 429; CAACH, 41) Consuming caffeine with ginseng increases the risk of overstimulation and gastro-intestinal upset. (BSH, 81; BHC, 116) Higher doses can over-stimulate and aggravate insomnia, irritability, depression, headache, palpitation, hypertension, and can cause tremor, euphoria, skin eruptions, menstrual abnormalities, diminished sexual function and weight loss. (BSH, 81; CAACH, 40). May reduce blood glucose levels, diabetic patients should consult with physician. (WHO, 176)
Licorice Glycyrrhiza glabra  Should not be taken concurrently with corticosteroid treatment. (WHO, 190; AEHD, 77) Concurrent use of furosemide may potentiate development of acute renal failure. (AEHD, 77) Potassium loss due to other drugs, e.g. thiazide diuretics, can be increased. With potassium loss, sensitivity to digitalis glycosides increases. (HM, 237; TGHM, 161; WHO, 190) Should not be administered in conjunction with spironolactone or amiloride. (WHO, 190) Insulin may be synergistic with glycyrrhizin in causing electrolyte disturbances and suppression of renin and aldosterone. (AEHD, 77) It is recommended that patients with cardiovascular or renal disease use licorice only under care of physician. (TCPHP, 232; PPP, 474) Patients prone to potassium deficiency are also advised not to use licorice. (TCPHP, 232; TGHM, 161) Treatment not to exceed six weeks. (TCPHP, 232; BSH, 58; TGHM, 162) Contraindications: cholestatic liver disorders, liver cirrhosis, hypertonia, hypokalemia, and severe kidney insufficiency. (HM, 236; BSH, 58; BHC,146; TGHM, 161; WHO, 190; AEHD, 72) Also contraindicated if there is edema or congestive heart failure. (PPP, 474) Ingestion of large amount can lead to severe hypertension, cardiac arrhythmias, cardiomyopathy, and cardiac arrest. (AEHD, 73; BSH, 58; BHC, 146; AEHD, 72) 
Marshmallow Althaea officinalis Absorption of other drugs taken simultaneously may be delayed. (BSH, 9; HM, 245, 247; ESCOPM, 1; TGHM, 166, 167) As a mucilage or respiratory demulcent, contraindicated or at least inappropriate in congestive bronchial, catarrhal and congestive conditions of the mucosa. (PPP, 169, 211) 
Oregon Grape Berberis aquifolium
Berberine, an alkaloid constituent of this herb, may potentiate other drugs which displace the protein binding of bilirubin. (PPP, 295) This herb is classified as a choleretic and cholagogue. It is either contraindicated or at least inappropriate in the following: (1) obstructed bile ducts, (2) unconjugated hyperbilirubinaemia, (3) acute or severe hepatocellular disease, (4) septic cholecystitis (where there is risk of peritonitis), (5) intestinal spasm or ileus, and (6) liver cancer. (PPP, 187) As an alterative, this herb may be provocative to skin disease, and care needs to be taken to reduce the prospects of exacerbations. (PPP, 254) 
Pau D'Arco Tabebuia avellanedae Patients on anticoagulant therapy should not be prescribed Pau DíArco due to the warfarin-like action of naphthoquinones at high doses. (PPP, 504) Contraindicated with anticoagulants. (PPP, 504) Adverse effects are not expected when consumed with the recommended dosage. (PPP, 500)
St. John's Wort Hypericum perforatum  None known. (ESCOPM, 2; TGHM, 215; HM, 363) May potentiate pharmaceutical MAO-inhibitors. (BSH, 62, 173) Recommend physician consultation when taken with MAO inhibitors, SSRIs, and tricyclics. (PPP, 549); Drugs for iron therapy Contraindicated in the treatment of serious depression with psychotic symptoms, suicidal risk or signs and symptoms that are so severe that they do not allow the patientís family or work involvements to continue. (PPP, 549) May cause mild stomach discomfort, skin rash, tiredness, fatigue, sleep disturbances, photosensitization is possible, especially in fair skinned individuals. (BSH, 62; TGHM, 215; HM, 363; PPP, 548; ESCOPM, 1996, 1) Caution advised in very severe debility, especially if associated with immune or digestive collapse, renal or hepatic failure, rampant cancer or strong regimes of chemotherapy. (PPP, 155) dermatologic and neurologic concern based upon case reports. (TCPHP, 301); Inhibits iron absorption
Sarsaparilla Smilax ornata Commission E advises of potential drug interactions with hypnotics, digitalis glycosides, and bismuth. However, no other reference substantiates these concerns. (BSH, 108) Risks: taking the herb may lead to gastric irritation and temporary kidney impairment [diuresis]. The absorption of simultaneously administered substances may be increased. The elimination of other substances (e.g., hypnotics) is accelerated. This can cause an uncontrolled condition of increased or decreased action of herbs taken simultaneously. (TGHM, 372)
Tribulus Tribulus terrestris  This herb may increase FSH in women, which in turn increases levels of oestrogen. (PPP, 46)  Due to the presence of saponins, this herb may be a gastrointestinal irritant. (PPP, 46)
Turmeric Curcuma longa
None known. (HM, 382; TGHM, 222) High doses should not be given to patients taking antiplatelet or anticoagulant drugs. (PPP, 578) Contraindicated in obstruction of bile passages; in case of gallstones, use only after consulting with a physician. (TGHM, 222; HM, 382; WHO, 121; PPP, 578) The herb should not be administered to patients who suffer from stomach ulcers or hyperacidity. (BSH, 39; HM, 382) Occasional cases of allergic dermatitis reported. (WHO, 121; PPP, 578) Patients applying topical doses should be cautioned against excessive exposure to sunlight. (PPP, 578) 
Valerian Valeriana officinalis  None known. (TGHM, 226; ESCOPM, 2; HM, 397) May increase the effects of CNS depressants or alcohol when taken together. (PPP, 587; AEHD, 172; WHO, 273) The herb may be expected to have at least an additive effect with barbiturates, alcohol, benzodiazepines, and other CNS depressants. (TCPHP, 64); diphenlydramine Can aggravate a sensation of tiredness or drowsiness, particularly in higher doses. (PPP, 587; WHO, 273) Overdose can result in blurred vision, erratic heart beat, headache, nausea, restlessness, visual illusions, even spasmodic movements. (PPP, 588; BSH, 120) Very large doses may cause bradycardia and arrhythmias, and decrease intestinal motility. (WHO, 274) Canada allows products containing valerian for use as sleeping aids and sedatives. (TCPHP, 64) Hepatic and neurologic concern based upon case reports, although in the case of alleged hepatotoxicity coingestants were involved. (TCPHP, 301)
Yohimbe Pausinystalia yohimbe Monoaminoxidase inhibitors Causes hypertension, insomnia, headache, and tremulousness
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