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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.

While there used to be a great divided exists a great divide 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 will expand as information is gathered from frequent updating on scientific studies for the medicinal plants.


Possible Herb-Drug Interactions
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.
Arnica (Mountain arnica): May reduce hypotensive effects; may potentiate anticoagulant effect of coumarin.
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.
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.
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.
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.
Dalandan (Sour orange): Study suggests it may increase blood levels of drugs (cyclosporine, felodipine, indinavir).
Dilaw (Tumeric): Tumeric might slow blood clotting and when taken with anticoagulants, medications that also slow blood clotting, mit might increase the chnaces of bruising and bleeding.
Durian: Hypothermic effect with paracetamol; High potassium content is a concern for patients with renal insufficiency or taking potassium supplements..
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.
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.
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
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.
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.
Luya (Ginger): Can affect anticoagulation therapy.
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.
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.
Paminta (Black pepper): Increased analgesic effect of Diclofenac.
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.
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.
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.
Suha (grapefruit): inhibits the absorption of some drugs.
Sulasi (Holy basil): Interaction with Glimepiride, a sulfonylurea used in the treatment of T2DM, necessitate dose readjustment of glimepiride.
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.
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.

Updated May 2017 / April 2017
September 2015



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