Wellness Learning Center
Botanical Medicine
Herb/Drug Interactions
Sue H. Mustalish, RN, HNC
Roger W. Mustalish, MPH, Ph.D.
"Above all, do no harm"
The above quote is part of the Hippocratic Oath, sworn to by all physicians; it is also a guiding principle for medical herbalists. Yet, this ancient admonition seems increasingly elusive, as evidenced by adverse drug reactions now being the fourth leading cause of death in the United States while injuring another 2 million individuals (Lazarou et al.). A case in point is Diane Ayres. Her husband, Stephen, recounts in his book, Bitter Pills: Inside the Hazardous World of Legal Drugs, her struggle to recover from serious side-effects, including acute delirium, after taking a single dose of Floxin for a urinary tract infection. Her story, and countless untold others, raises understandable concern within the health care profession. Even a casual glance at the Physicians' Desk Reference, or professional literature, reveals significant contraindications associated with the use of synthetic pharmaceuticals. Pelton et al provide a comprehensive list of nutrient depletions and subsequent health problems associated with H-2 receptor antagonists (e.g. Zantac, Pepcid); general antibiotics (e.g. penicillins, tetracyclines, co-trimoxazole, neomycin); salicylates (e.g. Bayer, Anacin) and tricyclic antidepressants (e.g. Adapin, Norpramin, Zonalon). However, while botanical medicines may represent a safer, more natural alternative to synthetic pharmaceuticals, as Hawkins stresses their potential to also cause undesirable side effects warrants forethought, too. Useful references addressing herbal contraindications include: Herbal Medicine (Blumenthal et al), Botanical Safety Handbook (McGuffin et al), Herbal PDR, and Herb Contraindications and Drug Interactions (Brinker). Now, add to this mix the increasingly widespread practice by individuals of taking both pharmaceuticals and herbal medicines simultaneously, and one can appreciate the need of nurses and other health care practitioners to be mindful of the medications being taken by their clients, and to be knowledgeable about herbal actions and possible interactions.
Four broad categories of herb/drug interactions can be identified (modified from Brinker):
- Inhibition of intestinal adsorption of pharmaceuticals
Hydrocolloidal Fibers. By creating increased viscosity and delayed gastric emptying, these botanicals may slow absorption of oral drugs and/or reduce serum nutrient levels. Examples include: Aloe gel, fenugreek seed, flax seed, oat seed, okra fruit, and psyllium seed husks.
Tannins and Salicylates. Both categories of compounds can precipitate alkaloid from botanical and pharmaceutical drugs (e.g. Atropa belladona, ephedrine), proteins (e.g. albumin), and metals (e.g. copper, iron) thereby slowing, reducing or blocking their absorption. Examples include: Alum root, black walnut leaves, raspberry leaves, tea leaves, and witch hazel leaves.
- Potentiation of Cardiotonic Medicines
Herbal Cardiotonics. Plants that contain steroidal cardiac glycosides, similar to digitalis, can create an additive effect leading to cardiac toxicity when taken along with digoxin, digitoxin, or other glycosides. Because of this toxicity, commercial preparations from these plants are generally not available except in homeopathic dosages. Examples include: Foxglove leaves, lily of the valley roots, and oleander leaves.
Potassium Depletors. When used chronically or in large doses, these plants can decrease serum potassium levels via the stool and/or urine. They are contraindicated with such drugs as furosemide. Examples include:
Laxatives: Aloes resin, rhubarb root, and senna leaves and pods.
Diuretics: Asparagus shoots, celery seed, corn silk, coffee beans, juniper berries, parsley fruit, tea leaves and watermelon seeds.
- Potentiation of Sedative or Tranquilizing Pharmaceuticals
Many plants are useful for promoting sleep, reducing muscle tension and mitigating anxiety. However, when combined with tranquilizers and antihistamine containing sedatives, sensory, cognitive or somatic impairment may occur. Thus, caution is suggested when driving, or operating machinery. Examples are: Kava-kava root, valerian root, wild lettuce and skullcap.
- Modification of Blood Sugar in Insulin-Dependent Diabetics
Hypoglycemic herbs. Many herbs are effectively used by Type II diabetics to lower blood sugar. However, their use by Type I diabetics potentially can cause fluctuations in blood sugar levels and modifications in insulin requirements. Examples include: barley sprouts, bilberry leaves, bitter melon, burdock roots, cucumber fruit, dandelion plant, fenugreek seeds, ginseng roots, onion, garlic, spinach leaves, and stinging nettle.
Hyperglycemic herbs. Any plants that raise blood sugar are contraindicated for diabetics. Other than those high in sugar or carbohydrates, additional plants to avoid are typically those containing caffeine, e.g. cocoa seeds, coffee beans, rosemary leaves and tea leaves.
While a great deal of attention is given to adverse herb/drug interactions, an awareness of an herb’s potentiation activity, can provide health care providers with a new tool. By carefully combining herbs and drugs, it is sometimes possible to achieve the desired effect at lower cost with smaller dosages while reducing side effects. Abernathy and McInnes each suggest just such a role for grapefruit juice. Likewise, Brinker reports that animal and human studies indicate milk thistle (containing three flavonolignans) may help prevent or reduce liver damage from medications that are metabolized in the liver. He also offers evidence demonstrating the increased efficacy of coal-tar dermal treatments for psoriasis when combined with allantoin derived from comfrey leaves and roots. Finally, he cites extended survival times of stomach cancer patients receiving chemotherapy along with injections of lentinan extracted from shiitake mushrooms.
So what is the bottom line? More research on herb/drug interactions is needed, especially on the unique role of whole plant extracts on drugs, rather than the tendency to compare single herbal active ingredients to their synthetic counterparts. But there is an emerging strategy to avoid herb/drug interactions. See Table 1.
Guidelines to Avoid Herb/Drug Interactions.
- View the client holistically and understand the underlying cause of the illness, not just how to suppress symptoms with drugs or herbs.
- Empower the client to be an active participant in their healing and establish effective communications with them, especially relating to their herbal supplementation practices while taking pharmaceuticals.
- Be knowledgeable about activities, side effects and potential herb/drug interactions. Report any occurrences of adverse effects.
- Encourage the use of costly, dangerous pharmaceuticals only as a last resort. Explore safer alternatives, especially those aimed at alleviating the underlying cause. For example, promoting effective stress reduction via exercise, counseling, and meditation rather than immediately resorting to drug or herbal therapies for symptom suppression.
- Take advantage of the potentiating effects of some herbs and use them to lower dosages and lessen side effects of pharmaceuticals.
Literature Cited
Abernathy, D. 1997. Editorial: Grapefruit and Drugs: When is Statistically Significant Clinically Significant? Journal of Clinical Investigation Vol. 99(10): 2297-2298.
Blumenthal, M., A. Goldberg, and J. Brinckmann, eds. 2000. Herbal Medicine. Newton, MA: Integrative Medicine Communications. 519 pp.
Brinker, F. 1997. Interactions of Pharmaceutical and Botanical Medicines. Journal of Naturopathic Medicine. Vol. 7(2): 14-20.
Brinker, F. 1997. Herb Contraindications and Drug Interactions. Sandy, OR: Eclectic Institute, Inc. 146 pp.
Hawkins, E. 1999. And the Good Herb Taketh Away. Nutrition Science News. Vol. 4(10): 482-486.
Lazarou, J, B. Pomeranz, and P. Corey. 1998. Incidence of Adverse Drug Reactions in Hospitalized Patients: a Meta-Analysis of Prospective Studies. Journal of the American Medical Association. Vol. 279(15): 1200-1205.
McGuffin, M., C. Hobbs, R. Upton, and A. Goldberg. 1997. Botanical Safety Handbook. Boca Raton, FL: CRC Press. 231 pp.
McInnes, K. 1998. Drug Interactions with Grapefruit Juice. Canadian Pharmaceutical Journal. April: 30-32.
Pelton, R., J. LaValle, E. Hawkins, and D. Krinsky. 1999. Drug-Induced Nutrient Depletion Handbook. Lexi-Comp.
Physicians’ Desk Reference. 1999. Montvale, NJ: Medical Economics Company. 2998 pp.
PDR for Herbal Medicine. 1998. Montvale, NJ: Medical Economics Company. 1244 pp.
