This is a partial list of herbs and herbal treatments with known or suspected adverse effects, either alone or in interaction with other herbs or drugs. Non-inclusion of an herb in this list does not imply that it is free of adverse effects. In general, the safety and effectiveness of alternative medicines have not been scientifically proven[1] and remain largely unknown.[2] Beyond adverse effects from the herb itself, "adulteration, inappropriate formulation, or lack of understanding of plant and drug interactions have led to adverse reactions that are sometimes life threatening or lethal."[3]
Most of the adverse effects stated in this list are associated with only a small percentage of cases; they should be understood as potential risks rather than as certainties.
| Name | Other common names | Scientific name | Adverse effects | |
|---|---|---|---|---|
| Aconite | monkshood, wolfsbane, aconitum | Aconitum spp. | Heart palpitations and arrhythmias, hypotension, nausea, vomiting, abdominal pain, respiratory system paralysis, death[4] | |
| Aloe vera juice | medicinal aloe | Aloe vera | "abdominal pain, diarrhea, potentially carcinogenic, with others can potentiate cardiac glycosides and antiarrhythmic agents" | |
| Anthranoid laxatives | "abdominal pain, diarrhea, potentially carcinogenic, with others can potentiate cardiac glycosides and antiarrhythmic agents" | |||
| Areca nut | betel nut | Areca catechu | "deterioration of psychosis in patients with preexisting psychiatric disorders"; known carcinogen contributing to cancer of the mouth, pharynx, esophagus and stomach when chewed.[5] | |
| Aristolochic acid (contained in herbs in the genus Aristolochia e.g. Aristolochia serpentaria (Virginia snakeroot), Aristolochia reticulata (Texas snakeroot) and in Chinese herbs such as Aristolochia fangchi and Aristolochia manshuriensis[6] (banned in China and withdrawn from Chinese Pharmacopoea 2005; Stephania tetrandra and Magnolia officinalis do not contain aristolochic acid). | Kidney toxicity associated with kidney failure; associated with development of cancer, particularly of the urinary tract, known carcinogen[7] [8] | |||
| Atractylate | Atractylis gummifera | Liver damage, nausea, vomiting, epigastric and abdominal pain, diarrhoea, anxiety, headache and convulsions, often followed by coma[9] | ||
| Ayurvedic Herbo-mineral (Rasashastra) Medicines | Heavy metal contamination[10] | |||
| Bitter orange | 'Fainting, arrhythmia, heart attack, stroke, death' | |||
| Broom | broom flower, dyer's broom, dyer's greenwood, dyer's weed, dyer's whin, furze, green broom, greenweed, wood waxen | Genista tinctoria[11] | Uterotonic properties, nausea vomiting, and diarrhea, contraindicated for pregnancy and breast feeding | |
| Buckthorn bark and berry | alder buckthorn | Rhamnus frangula | "abdominal pain, diarrhea, potentially carcinogenic, with others can potentiate cardiac glycosides and antiarrhythmic agents" | |
| Cascara sagrada bark | bearberry | Rhamnus purshiana | "abdominal pain, diarrhea, potentially carcinogenic, with others can potentiate cardiac glycosides and antiarrhythmic agents" | |
| Chaparral | creosote bush, gobernadora, larreastat | Larrea tridentata, Larrea divaricata | Liver damage, kidney problems, Hypotension in cancer patients | |
| Chinese herbal mixtures | Heavy metal poisoning | |||
| Coltsfoot | coughwort, farfarae folium leaf, foalswort | Tussilago farfara | Liver damage, cancer | |
| Comfrey | comphrey, blackwort, common comfrey, slippery root | Symphytum officinale | Liver damage, cancer | |
| Country mallow | heartleaf, silky white mallow | Sida cordifolia | "Heart attack, heart arrhythmia, stroke, death" | |
| Dan Shen | red sage, Chinese sage, tan shen | Salvia miltiorrhiza | Potentiates warfarin activity, leading to excessive anticoagulation and bleeding[12] | |
| Dong quai | female ginseng | Angelica sinensis | May induce uterine contractions; contraindicated when pregnant or nursing[13] | |
| European Mistletoe | common mistletoe | Viscum album | Toxic to cardio and central nervous systems, gastrointestinal bleeding | |
| Ephedra | ma huang | Ephedra sinica | Agitation and palpitations, "hypertension, irregular heart rate, insomnia, nervousness, tremors and seizures, paranoid psychosis, heart attacks, strokes, and death", kidney stones | |
| Flavonoids (contained in many medicinal plants) | Vitamin P, citrin | Flavonoids, bioflavonoids | Hemolytic anemia, kidney damage | |
| Germander | Teucrium | Liver damage | ||
| Ginger | Zingiber officinale | May increase the risk of bleeding | ||
| Ginkgo | gingko | Ginkgo biloba | Bleeding[14] | |
| American Ginseng | American Ginseng, Canadian Ginseng, Ginseng, Ginseng Root, North American Ginseng, Occidental Ginseng, Ontario Ginseng, Panax quinquefolium, Panax quinquefolius, Red Berry, Ren Shen, Sang, Shang, Shi Yang Seng, Wisconsin Ginseng[15] | Panax quinquefolius | "Hypertensive and chronotropic activities, may increase digoxin levels", diarrhea, itching, insomnia, headaches, nervousness, rapid heartbeat, hypertension or hypotension, breast tenderness, vaginal bleeding. Very rarely Stevens–Johnson syndrome, liver damage, severe allergy has been reported May lower blood sugar excessively in combination with diabetes medication. Contains a chemical linked to possible birth defects. May worsen hormone sensitive conditions such as breast cancer, uterine cancer, ovarian cancer, endometriosis, and uterine fibroids. Insomnia. | |
| Goldenseal | orangeroot, yellow puccoon | Hydrastis canadensis | Uterotonic | |
| Greater celandine | celandine | Chelidonium majus | Liver damage | |
| Guarana | Paullinia cupana | Agitation and insomnia | ||
| Guar gum | guaran | Obstruction of gastrointestinal tract | ||
| Gugulipid | guggal, guggul, Mukul myrrh tree | Commiphora mukul | "Headache, nausea, hiccups, diminished efficacy of other cardiovascular drugs including diltiazem and propranolol" | |
| Hawthorn | common hawthorn, may, mayblossom, maythorn, quickthorn, whitethorn, motherdie, haw | Crataegus monogyna | "Potentiates digitalis activity, increases coronary dilation effects of theophylline, caffeine, papaverine, sodium nitrate, adenosine and epinephrine, increase barbiturate-induced sleeping times" | |
| Horse chestnut | conker tree, conker | Aesculus hippocastanum | Liver toxicity, allergic reaction, anaphylaxis | |
| Kava | awa, kava-kava | Piper methysticum | Potentiates CNS sedatives, chronic use might cause a reversible dry skin condition.[16] | |
| Khat | qat | Catha edulis | Chronic liver dysfunction[17] | |
| Kratom | Mitragyna speciosa | Hepatotoxicity[18] | ||
| Liquorice root | Glycyrrhiza glabra | Hypokalemia, hypertension, arrhythmias, edema | ||
| Lobelia | asthma weed, pukeweed, vomit wort | Lobelia inflata | Toxicity, rapid heartbeat, hypotension, coma, death | |
| Milk thistle | Marian thistle | Silybum marianum | Mild laxative, allergy | |
| Pennyroyal | Mentha pulegium | Liver damage | ||
| Peony | Bai Shao, Chi Shao, Chinese peony, common peony, coral peony, Cortex Moutan, European peony, Jiu Chao Bai Shao, Moutan, Mu Dan PI, peony flower, peony root, piney, radix peony, red peony, Shakuyaku, Shao Yao, tree peony, Ud Saleeb, Udsalam, Udsalap, White Peony[19] | Radix Paeoniae, Radix Paeoniae Alba, Radix Paeoniae Rubra, Paeonia, Paeonia alba, Paeonia lactiflora, Paeonia mascula; Paeonia obovata; Paeonia officinalis; Paeonia suffruticosa, Paeonia veitchii, Paeoniae Flos, Paeoniae Radix | May slow clotting; contraindicated for people with bleeding disorders and before and after surgery. May induce uterine contractions; contraindicated when pregnant or nursing. | |
| Pyrrolizidine alkaloids (contained in comfrey, borage, senecio, coltsfoot, and others) | Liver damage | |||
| Reserpine | Rauvolfia serpentina | "Sedation, inability to complete tasks, mental depression, nasal congestion, increased gastric secretion and mild diarrhea" | ||
| Safrole | Sassafras albidum | Liver damage | ||
| Saw palmetto | Serenoa repens | "rare and mild gastrointestinal upset, headaches, diarrhea, gynecomastia, paroxysmal atrial fibrillation, ventricular rupture and death in one patient" | ||
| Senna | Egyptian senna | Senna alexandrina (Cassia senna) | "abdominal pain, diarrhea, potentially carcinogenic, with others can potentiate cardiac glycosides and antiarrhythmic agents", liver damage | |
| St John's wort | Tipton's weed, Klamath weed | Hypericum perforatum | Photosensitization, GI disturbances, "allergic reactions, fatigue, dizziness, confusion, dry mouth" | |
| Valerian | garden valerian, garden heliotrope, all-heal | Valeriana officinalis | "drowsiness, GI upset, headache, palpitations, insomnia", oversedation, overstimulation[20] | |
| Vasambu | sweet flag | Acorus calamus | Vomiting and nausea[21] | |
| Yohimbe | yohimbine | Pausinystalia johimbe | rapid heart rate, hypertension, hypotension, heart problems, death |
| Name | Other common names | Scientific name | Drug | Adverse effects | |
|---|---|---|---|---|---|
| Cinchona bark | Cinchona pubescens | Warfarin | Possible additive effect | ||
| Chamomile | Blood thinners[22] | ||||
| Devil's Claw | grapple plant, wood spider | Harpagophytum | Warfarin | Additive effect | |
| Ephedra | Ephedra | Caffeine, decongestants, stimulants | Increases sympathomimetic effect of ephedra | ||
| Feverfew | featherfew | Tanacetum parthenium | Aspirin | Additive effect | |
| Garlic | Allium sativum | Warfarin | Additive effect | ||
| Ginger | Zingiber officinale | Warfarin | Additive effect, causes iris bleeding | ||
| Ginkgo | gingko | Ginkgo biloba | Aspirin, warfarin, ticlopidine, clopidogrel, dipyridamole, garlic, vitamin E | With aspirin – retards aspirin absorption | |
| Ginseng | Panax ginseng | Warfarin | |||
| Papaya extract | Carica papaya | Warfarin | Damage to GI tract mucous membranes | ||
| Kava | kava-kava | Piper methysticum | Sedatives, sleeping pills, antipsychotics, alcohol | ||
| Milkvetch | Astragalus | Astragalus may interact with medications that suppress the immune system, such as cyclophosphamide.[23] | It may also affect blood sugar levels and blood pressure. | ||
| Pineapple enzyme | Ananas comosus | Bromelain | "Diarrhea, increased tendency for bleeding if used simultaneously with anticoagulants and inhibitors of thrombocytic aggregation due to modulation of the arachidonate cascade" | ||
| Psyllium seed | Plantago spp | Coumarin derivates | Retards absorption of drug | ||
| St John's wort | Tipton's weed, Klamath weed | Hypericum perforatum | Antidepressants, warfarin, protease inhibitors for HIV, birth control, some asthma drugs, and many other medications |