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Herb-Drug Interactions

Fed by the insatiable needs of the New-Age must-feel-good self-medicating generation, the past decade has seen an explosion in the commerce and popularity of alternative therapies and countless over-the-counter supplements and herbal products—a multibillion-dollar industry with little or no control on uniformity and purity. Not classified as "drugs," herbals and supplements fall out of the umbrella of consumer protection. Contamination with herbicides, pesticides, heavy metals, molds and toxins have been reported. The active ingredients may vary from brand to brand—and in some, none at all. Some may contain ingredients with undesirable effects.

A great divide exists between pharmaceutical medicine and alternative medicine—the former often looks at alternative modalities with disdain, while the alternativists reject western therapies for its expense and toxicity—the commerce of alternative medicine has lured many physicians into a merging of prescription medicine with herbals and supplements. Talk-Radio medicine—seemingly informational for medical disease, but often a source of misinformation—often segue to the selling of herbal supplements, with hardly any caution on the possible interactions between herbs and drugs.

The increased commerce and popularity of alternative herbal therapies has brought added concern of unfamiliar herb-drug interactions in the already complicated world of pharmaceutical drug-drug interaction. Adding to the problem, patients are often hesitant to inform their physicians about their use of herbal supplement. Often the patients are themselves grossly uninformed of the side effects of herbal supplements they are using or their possible herb-drug interactions, indulging in it because of the word-of-mouth promise and snake-oil promotions.

Sadly, in time-constrained ka-ching medicine, physicians do not have the time to inquire into patients' alternative medicine use. Even if they do, physicians are usually uninformed, unable to provide the necessary guidance and information to assist patients in maneuvering through the confusing maze of alternative and supplementary therapies and their potential interaction with prescription drugs.

In my unending effort of updating the studies on medicinal plants, I am often filled with wonder on the treasure trove of herbal medicine, the studies that support the folklore of its use, and the its untapped potential. But while many plants—leaves, roots, seeds, and fruits—are wonderful sources of natural antioxidants and constituents that could potentially benefit the prevention and treatment of many medical diseases, there are some that can negatively impact pharmaceutical therapies through herb/drug interactions.

Some herbal therapies and supplements can increase or decrease the effects of anticoagulant (blood thinning) treatment, augment the hypoglycemic effects of antidiabetics and the hypotensive effects of antihypertensive drugs. Fruits can affect blood sugar levels in diabetics, dangerously increase potassium levels in patients with renal disease. Some plants parts—flowers, leaves, seeds, fruits—have reported toxicities, unknown to many users.

This page will focus on information on herb-drug interactions. While some are from human clinical studies and observations, many are from animal studies. The list is, of course, incomplete but updated as new information is gathered from frequent updating on scientific studies for the medicinal plants.

Possible Herb-Drug Interactions
Abukado (Avocda): Reported interaction with warfarin (Coumadin). It might decrease the effectiveness of coumadin and increase the risk of clotting.
Alfalfa: Reported interaction with anticoagulant therapy; toxicities, pregnancy concern, and bacterial contamination.
Alpasotis / Wormseed: Chenopodium oil may interact with drug increasing sensitivity to sunlight (photosensitizing), for example: Cipro, Levofloxacin, Septra, etc.
Ampalaya (Bitter melon): Antidiabetic synergism with Metformin and Glibenclamide.
Anis / Haras (Fennel): Because of inhibition of cytochrome P450 3A4 (CYP3A4), pharmacokinetic parameters of drugs metabolized by this isoenzyme may be affected. A significant interaction between ciprofloxacin and F. vulgaris has been demonstrated.
Apatot (Noni): Moderate drug interactions. Ace inhibitors interact with NONI. Some blood pressure medications can increase the potassium levels in blood, and taking NONI juice can further increase potassium in the blood. Noni might also cause harm to the liver, and should not be taken with medications with potential liver effect. (more)
Acerola (Barbados cherry): Moderate interactions with flluphenazine (may decrease how well Prolixin wells), warfarin (may decrease the effect of coumadin); minor interactions: its high vitamin C content may increase the absorption of estrogen and increase its side effects.
Arnica (Mountain arnica): May reduce hypotensive effects; may potentiate anticoagulant effect of medications that slow blood clottings and increase the chance of bruising and bleeding.
Arugula (Salad rocket): The vitamin K content of arugula (110-130 µg/100 g) may cause a problem of anticoagulant resistance for patients taking warfarin (Coumadin) for the prevention of venous or arteria thrombosis.
Asparagus: Has moderate interactions in lithium. Taking asparaagus with lithium might decrease the excretion of llithium, increasing drug levels and cause serious side effects.
Ayapana (White snakeroot): Leaves contain naturally occurring coumarins with blood thinning and anti-coagulant effect. A patient on blood thinning medications should avoid the concomitant use of ayapana and should consult a physician.
Baai (Kudzu): Interaction with oral contraceptives, estrogen, methotrexate, anticoagulants, tamoxifen, and antidiabetic pills.
Bael (Stone apple): An aqueous extract of A. marmelos showed agonistic activity on cholinergic, serotonergic and adrenergic receptors on isolated rat ileum and aninal tissue preparations.
Balimbing (Star fruit): Fruit juice has strong human cytochrome P450 inhibition. Aqueous extract also shown to have hypotensive effect.
Banaba (Queen's flower): Banaba interacts with antidiabetic medications. It can lower blood sugar and may cause blood sugar to go too low when taken together with antidiabetic medications.
Bay leaf (Laurel) - Increases effects of narcotic analgesics and sedatives.
Bawang (Garlic): (1) Known to have antiplatelet properties' can affect anticoagulation therapy. (2) Study suggests alteration of Metformin pharmacokinetics with increased availability.
Bunga (Areca nut palm): Moderate interaction concerns with: (1) Drying medications like atropine and scopolamine, antihistamines, and antidepressants. (2) Procyclidine (3) Drugs for glaucoma and Alzheimer's disease.
Celery: There are anecdotal reports on the potential interaction between thyroxine and celery seed tablets.
Cloves: Minor interactions with medications that slow blood clotting (anticoagulants, and antiplatelet drugs). Taking cloves with these medications may increase the chances of bruising and bleeding.
Curly dock (Rumex): Interacts with digoxin, diuretics, and warfarin; may cause decrease in body potassium and increase bleeding.
Dalandan (Sour orange): Study suggests it may increase blood levels of drugs (cyclosporine, felodipine, indinavir). Major interactions with medications taken for depression (MAOs) and midazolam (Versed). Moderate interactions with caffeine, dextrometorphan, felopidine, etc. (MedMD)
Dilaw (Tumeric): Tumeric might slow blood clotting and when taken with anticoagulants, medications that also slow blood clotting, might increase the chances of bruising and bleeding.
Durian: Suspected hypothermic effect with paracetamol; High potassium content is a concern for patients with renal insufficiency or taking potassium supplements.Also, a disulfiram-type reaction with alcohol.

Eucaliptos / Eucaluptus: Eucalptus may augment the blood sugar lowering effect of antidiabetic drugs. Medications changed by the liver through Cytochrome P459 system interacts with eucalyptus, increasing their effects and side effects.

Haras / Fennel: Haras may decrease absorption of ciprofloxacin; decrease the effectiveness of tamoxifen; might decrease the effectiveness of birth control pills.
Goji berry / Lycium barbarum: Possible interaction with anticoagulan warfarin, which may increase the risk of bleeding.
Granada (Pomegranate): Possible interactions with various drugs: (1) May increase the effect of antihypertensive ACE inhibitor and cause low blood pressure (2) Statins: one case report of rhabdomyolysis after taking rosuvastatin and pomegranate juice (3) Warfarin (coumadin): Pomegranate may interact with coumadin and increase risk of bleeding.
Gulipas / Indian Ephedra: Sida cordifolia can interact with many cardiac medications, methylxanthines, stimulant drugs. Moderate interaction may also be seen with dexamethasone, ergot derivatives, MAOs, and antidiabetic drugs.
Horsetail : May interact with lithium, decreasing its excretion and increasing its effects. Also might have a diuretic effect.
Hydrangea / Mopheads: May interact with lithium, decreasing its excretion and increasing its effects. Also might have a diuretic effect.
Kabling-gubat (Java tea): Lithium interacts with Java tea. Java tea might decrease the excretion of lithium. The increase in its blood level may require an adjustment of its dose.
Kakaw (Cacao): Studies suggest several cacao/drug interactions related to the caffeine content, antiplatelet and anticoagulant effect, and possible antihypertensive effect, among others.
Kaki / Oriental persimmon: May potential the antihypertensive effects of drugs like captopril, enalapril, losartan, valsartan, diltiazen, amlodipine, HCTZ, furosemide, along others.
Kamias (Bilimbi tree): May potentiate anticoagulant therapy because of high level of oxalic acid in A. bilimbi. Oxalate presumbly binds to blood calcium, removing calcium ions from the blood, and inhibiting the clotting process
Kape / Coffee: Major and minor drug interactions.
Karipata (Curry leaf): Potentiation of Diclofenac effects and blood sugar lowering effects. Has syngergistic hypotensive effect with amlodipine.
Kangkong (Water spinach): Leaf extract may potentiate anxiolytic effects of CNS depressants.
Kasubha (Safflower): Moderate interactions with anticoagulants and antiplatelet drugs. Large amount of safflower can slow blood clotting.
Katigbi / Job's tears: Interacts with antidiabtic drugs and may cuse blood sugar to go too low.
Komintana (Ink nut): A report describes two relapses of depression in a patient well controlled with sertraline monotherapy in close temporal relationship with starting an ayurvedic herbal mixture. The herbal plant responsible for the interaction is suspected to be either Terminalia chebula or Commiphora wighteii.
Komprey (Comfrey): Hepatotoxic drugs interacts with comfrey. Taking comfrey with drugs that might harm the liver can increase the risk of liver damage. Medications that increase breakdown of medications by the liver (cytochrome P450 3A4 (CYP3A4) inducers) interacts with comfrey.
Kuasia (Bitter wood): Reported interaction with digoxin (Lanoxin) and diuretics. Also reported to increase stomach acid, decreasing the efficiency of antacids and proton pump inhibitors.
Lagundi (Five-leafed chaste tree) may decrease the plasma concentration of paracetamol.
Lanting (Plantain): Moderate interaction concerns with warfarin. Plantain contains large amounts of vitamin. By helping the blood clot, it might decrease the effectiveness of warfarin (coumadin). Dose of coumadin may need to be changed.
Lavandula may potentiate effects of antidepressants and anxiolytics.
Licorice / Anis: Major and moderate interactions with blood thinners (coumadin), digoxin, estrogen, diuretics, antihypertensives, and many medications affected by hepatic cytochrome system.
Lubigan / Sweet flag: Has moderate drug interactions: (1) MAO, medications for depression, for ex. Nardil (phenelzine), Parnate (tranylcypromine. (2) Sedatives, CNS depressants. Minor interactions with antacids, medications that decrease stomach acid (H2 blockers and proton pump inhibitors).
Luya (Ginger): Can affect anticoagulation therapy and medicines that lower blood pressure.
Malungay (Miracle tree): Moringinine, a hypotensive component.
Mangostana (Mangosteen): Herb-drug interactions are reported in (1) chemotherapy (2) calcineurin inhibitors, and (3) cytochrome P450 substrates.
Marjoram: Potential interaction with lithium. Marjoram may decrease excretion of lithium and increase the potential oflithium side effects.
Morera (Mulberry): Study showed mulberry significantly reduced the bioavailability of CSP (cyclosporine), a potent immunosuppressive used in transplant patients.
Neem (Holy tree): Neem may increase blood lithium levels by decreasing the body's ability to get rid of lithium. Neem may decrease blood sugar, interacting with diabetic medications to lower blood sugar further.
Nipai (Cowhage): Increase with antidepressants and antihypertensives.
Palong-manok (Red cockscomb): Moderate drug interactions: clozapine, estrogen, dipyridamole, MAO inhibitors, theophylline, lithium, hypoglcemics, among others.
Paminta (Black pepper): Increased analgesic effect of Diclofenac. (•) Moderate interactions with lithium, with increase lithium levels in the body. Pepper might also affect Cytochrome P450 3A4, and increase the side effects of some medications like lovastatin, ketoconazole, itraconazole, fexofenadine, triazolam, etc. It may affect medications moved by pumps in cells (P-glycoprotein substrates). Pepper might increase the absorption of phenytoin, propranolol, rifampin, theophylline, and carbamazepine, and increase the risk of side effects.
Pansit-pansitan (Shiny bush): Hypotensive effect and cytochrome P450 inhibitory effect.
Papaya (Carica papaya): (1) Papaya may affect the hypoglycemic activity of antidiabetics. (2) It may also increase the effects of warfarin (Coumadin), and increase the chances of bleeding and bruising. It may necessitate the change in coumadin dose.
Parsley: Large amount may increase blood clotting and interfere with the blood thinning effects of warfarin (Coumadin). Also, has a potential to augment diuretic and hypotensive therapies.
Pasau (Red juite): Synergism or antagonism with antibiotics.
Pasyonaryo (Passion fruit): Moderate interaction with sedative medications causing sleepiness and drowsiness.
Pinya (Pineapple): Pineapple has moderate interaction concerns. Amoxicillin interacts with bromelain; bromelain increases amoxicillin levels in the body, increasing effects and side effects. Bromelain may slow blood clotting; when taken with anticoagulants it may increase the chances of bruising and bleeding.
Romero (Rosemary): Rosemary can affect the activity of various medications: anticoagulants (aspirin, coumadin, clopidogrel), ace inhibitors (lisinopril, captopril, enalapril), diuretic, lithium.
Roselle (Red sorrel): Hypotensive effect may potentiate antihypertensive medications. Studies in healthy volunteers showed alterations in chloroquine, acetaminophen and diclofenac pharmacokinetics. The plant can also increase the diuretic effect of hydrochlorothiazide. s
Sabila (Aloe vera): Aloe may increase the risk of bleeding and should be taken with caution by patients with bleeding disorders or taking drugs that increase the risk of bleeding.
Sage: Possible interaction with drugs metaboized by the liver through induction of CYP 2E1 protein. Also, sage tea lowers fasting glucose in mice and has a diuretic effect.
Sarsaparilang-china (Sarsaparilla):  Interacts with digoxin (Lanoxin) increasing the absorption of digoxin. Sarsaparilla might also decrease the elimination of lithium from the body.
Stevia and hypotensive medications.
Sibuyas (Onion) and hypotensive medications.
Sinamomo / Henna:  Potential for moderate interaction with lithium. Henna can decrease how the body gets rid of lithium. Dose adjustment of lithium may be necessary.
Sinta (King of Bitters): Hypotensive, anticoagulant, and immune system effects.
Subsuban / Smartweed: Moderate interaction with warfarin. The plant contains large amounts of vitamin K which helps blood clotting. Warfarin is used to slow blood clotting. Therefore, subsuban might decrease the effectiveness of warfarin (coumadin).
Suha (grapefruit): inhibits the absorption or metabolism of some drugs.
Sulasi (Holy basil): Interaction with Glimepiride, a sulfonylurea used in the treatment of T2DM, necessitate dose readjustment of glimepiride.
Tambo  (Common reed): Moderate interactions reported. Lithium interacts with reed herb. It may decrease the excretion of lithium, increase its body levels and result in side effects.
Tanglad (Lemon grass) (1) May interfere with actions of some chemotherapeutic agents. (2) Avoid during pregnancy as high doses of citral and myrcene has cause birth defects in rats. (3) Citral in essential oil shown to induce GST. (4) ß-myrcene in lemongrass can interfere with cytochrome P450 liver enzymes. (MSKCC)
Tantanduk (Solidago virgaurea) may increase effect of diuretics.
Tarragon (Artemisia dracunculus): Used as anticoagulant in some cultural medicinal systems. Study of leaf extract showed anticoagulant activity., which raises concern for patients on anticoagulant therapy.
Tonghoy (Watercress): Moderate drug interactions with chlorzoxazone (Parafon Forte), lithium and warfarin.
Ulasimang-aso (Water hyssop): Inhibition of Cytochrome P450 Enzymes
Upang (Parkia speciosa) may increase liver drug metabolism.

Please click on plant names to go to specific plant page for more detailed information on studies, interactions, and sources.

© Godofredo U. Stuart Jr., M.D.

Last Update October 2022
September 2015

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