Author(s): Hue C. Thai, ND

Date Authored: September 1, 2004

Chinese herbal store
Chinese herbal store.

Herbal medicine has been an essential component of oriental medicine (OM), which has existed for over two thousand years. Guided by principles of Yin Yang, Five Elements, Organs and Meridians, the practice of oriental herbal medicine has not changed significantly (For more information on TCM theories, see Traditional Vietnamese Medicine). Herbal prescriptions comprise the vast majority of OM practice in China and Southeast Asia. Many city hospitals in China, Taiwan, and Korea have integrated clinics with dispensing labs that prepare herbal concoction. Scientific verification and applications beyond traditional prescriptions are beginning to be explored in the West.

For example, typing Chinese herbal medicine and Chinese herbal medicine AND pharmacology on Science Direct yielded 180 and 80 studies respectively. A similar search on showed a total of 524 studies; narrowing this search to Chinese herbal medicine and cancer resulted in 110 articles. Among this research includes documentations on herb-herb and herb-drug interactions.

This article focuses on commonly recognized Western botanicals as well as Chinese herb-drug interactions. It is hoped that this area of medicine which heavily depends on the cooperation of supplement/pharmaceutical industry, patients, and practitioners across specialties will mature to the point where one can safely go back and forth between traditional and modern medicine. Until then it is hoped that clinical guide such as this will help avert unnecessary interactions.

While literature emphasizes recent development in this area, it is worthy to acknowledge that herbal interactions were documented in ancient traditional TCM texts, by case studies and traditional theories. For example, in all formulae, warm herbs are balanced by cool herbs and vice versa. TCM herbalists have to carefully prescribe formulae based on disease manifestation and the patient’s energy ‘Qi’. Therefore, cold or hot drugs are rarely recommended for extended use-it is believed that they can deplete the body’s energy ‘Qi’. In Western medicine, laxatives and steroids are typical examples of cold and hot drugs. In addition to utilizing the herbs’ energetic property TCM practitioners also rely on the tastes of an herb as part of a therapeutic guide. For example, sweet herbs like licorice (glyccerhiza) are thought to be neutral and nourishing so it is often used in TCM herbal formulae to ameliorate side effects of other ingredients.

Traditional herbal texts recognized a number of herb-herb interactions as summarized below:

18 Incompatible Combinations

This includes three herbs (aconite, licorice, and veratrum) with 6 other herbs.  Their combinations would lead to herb-to-herb interactions and/or toxicity.

R. Glycerrhiza (Gan Cao)
Incompatible combinations
R. Euphorbiae Kansui (Gan sui), R. Euphorbiae seu Knoxiae (Da ji), Fos Geukwa (Yuan Hua), and
Herba sargassum (Hat zao)
Rhizoma Aconite (Wu tou)
 Bulbus fritillariae cirrhosac (Chuan bet mu), bulbus fritillariae thundergii (Zhe bet mu), Fructus trichosanthis (Gua leu), Rhizoma pinelliac (Ban xia), R. Ampelopsis (Bat lian), and Rhizoma bletillae (Bat ji).
Rhizoma et Radiz veratri (li lu)
 R. ginseng (Ren shen), R. Glehniae (Bet sha shen),
R. adenophorae (Nan shi shen), R. scrophulariae (Xuan she), R. paeoniae alba (Bat shao), R. paeoniac Rubra (Chi shao), and Herba asari (Xi xin).

Herbs with Teratogenic (Birth Defect) Effects

Hirudo seu whitmania
Shui zhi
MoschusShe xiang
MulabrisBan mao
Racix wuphorbiae
Da ji
Radix phytolaccae
Shang lu
Rhizoma sparganii
San leng
Rhizoma zedoariae
 E Zhu
Semen crotonis
 Ba dou
Semen pharbitidis
 Qian niu zi
Tabanus Meng chong

Herbs with Potential for Toxic Effects

These herbs are very strong Qi and Blood movers and can certainly cause side effects if used inappropriately.  They should also be avoided during pregnancy.

Semen persicae
Tao ren
Flos carthami
Hong hua
Rhizoma and Radix Rhei
Da huang
Fructus aurantii
Zi shi
Radix aconite
Fu zhi
Rhizoma zingiberis
Gan jiang
Cortex cinnamomi
Rou gui

Oriental herbal medical principles are fascinating and cannot be fairly addressed in this space. In general TCM herbal formulation often consists of 4-12 ingredients. Each herb plays an important role in the delivery and action of the formula. For example, certain ingredients assist in delivering the main herb to the organ or meridian while other ingredients act to reduce the side effects or to augment the desire effect. Oriental herbal medicine utilizes plants, minerals, insects, and animal products. Rarely do we find herbs being prescribed as a single agent.

However, consuming herbal medicine has not been without risks. Some Chinese herbs have been reported to contain heavy metals and/or adulterated with western drugs. For example, PC-SPES was recalled in California because it may have been contaminated with warfarin, alprazolam, and diethylstilbesterol (10).

Recent national surveys have shown that trends for complementary and alternative (CAM) usage have increased steadily among adults over the past 50 years. About 60 million Americans (1 in 5) use CAM therapy, and this trend is expected to significantly increase if insurance coverage for CAM increases in the future. It was estimated that 20% of patients regularly taking prescription drugs were also taking herbal or nutritional supplements, suggesting that about 15 million Americans are at potential risk for herb-drug interactions. Also, about a third of patients reported they seek CAM therapies for health promotion and disease prevention (1,2).

These studies were conducted among English speakers. Although no formal studies to date exist for ethnic minorities, it is expected that a higher percentage of Asian Pacific Islanders rely on their traditional herbal medicine and that many of them use both traditional and Western medicine concurrently or even interchangeably. 

Evidence for herb-drug interactions in humans has been inconsistently reported through case studies. One review 2/3 of the 108 case reports was classified as ‘unable to be evaluated’, which meant they lack critical information to explain other possibilities. For example, many the case reports focused solely on the agents involved and failed to include relevant information such as: patient history; concurrent diseases, conditions, or medication associated with adverse event; concomitant medications; description of interaction; alternative explanations; chronology, and time sequence of drug administration etc (3,4).

One of the challenges in integrative medicine at the presence is that most supplements available over-the-counter are not standardized.  Purity and potency standards are only available for a small selection of herbs. To further complicate this matter, patients may take supplements from different manufacturers (5).

Likewise similarities in names and appearance have caused some Chinese herbal products to contain misidentified plants. Pharmaceutical drugs and a significant level of heavy metals were also found in some herbal patents (4). Without a standard for purity and potency, the possibilities for interactions increase greatly for drug-herb, herb-herb, or reactions to contaminants. Besides posing risks of toxicity for patients, it is also difficult to verify reports on herb-drug adverse reactions due to numerous unknown variables.

The greatest potential for adverse effects between herb-drug combinations occurs when the followings are combined:

  • Sympathomimic (anti-seizure), and Cariovascular drugs: Ephedra (Ma huang) contains ephedrine, and pseudoephedrine that interferes with this class of drugs.
  • Diuretic drugs: A variety of herbs can increase or decrease this effect.  The most commonly used oriental herbs for their diuretic effects include:, Polypori Umbellati (Zhu ling), Semen plantaginis (Che qian zi), and Alismatis orientalis (Ze xie), Akebia trifoliata (Mu Tong).
  • Anti-diabetic drugs: Anemarrhena asphodeloidis (Zhi mu), Gypsum fibrosum (Shi gao), Scrophularia ningpoensis (Xuan shen), Atractylodes (Cang Zhu), Dioscorea oppositae (Shan yao), and Astragalus membranacei (Huang qi).
  • Anti-coagulating drugs: Because Coumadin (Warfarin) interacts with a wide range of herbs, it is best to avoid combining Coumadin with all herbs unless the patient has guidance from an experienced health professional. TCM herbs with the greatest potential for interfering with anti-coagulants includes: Salviae miltiorrhizae (Dan shen), Angelica sinensis (Dang gui), Ligustici chuanxiong (Chuan xiong), Persicae (Tao ren), Carthamus tinctorii (Hong hua), and Hirudo seu whitmania (Shut zhi). Likewise, patients should also monitor their green vegetables intakes when they are on anti-coagulant therapy.

In addition to the above guide and case reports, it is possible to predict when herb/drugs interact by knowing their pharmacokinetic properties, and their pharmacodynamic behaviors. For our purpose, pharmacokinetic properties entail changes in absorption, metabolism, and elimination of the drugs/herbs whereas pharmacodynamic behaviors refer to how the herb/drug interacts inside the body (synergistic or antagonistic).In general, herb/drug that alters the stomach pH (anti-acids), or intestinal motility (laxatives) will have an effect on absorption. Drug/herb metabolism occurs principally in the liver.

The duration (life-span) of an herb or drug in the body depends on whether the liver’s metabolism is induced or inhibited.  An herb lasts longer in the body if its metabolism is inhibited by another drug; likewise, it is excreted faster if one’s liver metabolism is induced. Further, drug/herb elimination primarily occurs at the kidneys and is affected by the individual’s kidneys function or by drugs’ toxic side effects.  Lastly, the extent to which an herb-drug interacts depends on the individual’s health condition, age, body weight, metabolic rate, and dosage (11).

Commonly Used Herbs Taken by Older Adults and Potential for Herb-Drug Interactions

Please refer to the sidebar for a PDF table of commonly used herbs and potential drug interaction.

(5,7,8,9)  As no list is complete, please consult with yoru provider if you plan to combine herbal/supplements with your medication.

In summary, patients should not try to mix drugs that have a narrow therapeutic range (digitalis, theophylline, lithium, and warfarin) with potassium lowering herbs (licorice, and aloe), herbal stimulants (ephedra, caffeine, guarana, green tea), and antiplatelet herbs (Ginkgo, bilberry leaf, ginger, black cohosh, and Chamomile) (11).

Just as important, if patients insist on integrating herbal medicine they must be taking their medication and herbs consistently in order to avoid severe under or overdose.

Using Foods to Balance Internal Disharmonies

In addition to herb-drug interactions, food can and do also interact with medication. Traditional Chinese medicine views food the same way it views medicine. For example, all foods and drinks are classified by their energetic properties such as hotwarm, neutral, cool, and cold (Yin and Yang). Further, foods are also graded by their tonic potential versus their draining effects on the body such as excessive heat, cold, damp, or dry. For example, rice is considered a tonic whereas cream is considered cold and damp. Thus, TCM thinks about food as medicine and their potential for benefits as well as interactions with herbal therapy. When a patient with excessive heat, cooling herbs are prescribed and instructed to avoid dry or hot food i.e. chips, deep-fried food, or spicy food.  Instead, the patient is advised to eat mung bean or mung bean sprouts. See Traditional Vietnamese Medicine  for more information on food as medicine.

Working with Patients who use Complementary and Alternative Medicine (CAM) and Conventional Medicine

With no clear guidelines for integrating CAM and conventional medicine, it is important for clinicians to foster an open dialogue with their patients. Eisenberg and colleagues reported that about 60% of the people surveyed did not discuss their CAM use with their primary care physicians (2). This lack of communication is expected to be more prevalent among immigrant communities due to language and cultural barriers. For example, many patients do not want to appear disobedient toward their providers by admitting that they are seeking other treatments, or think their providers care or need to know about their traditional practices.

Additionally, providers should be aware of reasons why their patients seek out CAM therapies. For example, 1) conventional therapies no longer provide relief or are producing unwanted side effects; and 2) no specific conventional therapy exist or the treatment plans are contrary to patient’s belief (6). Sometimes, a misunderstanding of the instruction of how to take the medicine, urgency of their conditions, or difficulties in filling the prescriptions can pose barriers for proper health care among immigrant communities.

Further, since CAM therapies have been an integral part of Southeast Asian’s health promotion and health maintenance practice, they do not generally associate potential for toxicity when combining CAM therapies with western drugs. Hence, providers should approach this discussion with sensitivity and openness (6).

Below are suggestions for exploring CAM therapies with Vietnamese patients:

Acknowledge that certain traditional health practices are common in their communities. For example, in Southeast Asia, ‘coining’ and ‘cupping’ are often used at home for minor aches, pain and colds. These techniques often leave bruise-like appearances on the skin.  Herbal tonics and dietary therapies are also commonly used for health maintenance. Some therapies clearly offer relieves, others are harmful especially when combined with western medication. The effects of combining both traditional and conventional therapies may take weeks or months to be apparent. Certain combinations can be detrimental.

Integrative medicine is a young practice, still needing a safe practice guideline, and resources for clinicians and patients alike. When working with patients utilizing CAM and western medicine, a step-by-step strategy is recommended. This includes: 1) Asking patients to identify the principle complaint and maintaining a symptom diary; 2) Discussing patient’s expectations and preferences, and reviewing safety and efficacy issues; 3) Identifying a suitable licensed provider; 4) Establishing a treatment strategy with CAM provider and requesting documentation; and 5) Scheduling follow-up visit to review treatment plan (6).


  1. Eisenberg, M. David, M.D; et al. Unconventional medicine in the United states. N England J Med. 1993 ; 328 :246-252.
  2. Eisenberg, David M. M.D; et al. Trends in Alternative Medical use in the United States, 1990-1997: Results of a Follow-up National Survey. JAMA, November 11, 1998-Vol 280, No. 18.
  3. Fugh-Berman, Adriane and Ernst E. Herb-drug interactions: Review and assessment of report reliability. Blackwell Science Ltd Dr J Clin Pharmacology, 2001-Vol. 52; 587-595.
  4. Fugh-Berman, Adriane. Herb-Drug interactions. Lancet, 2000; 355: 134-38
  5. Cupp, Melanie J. Pharm.D. Herbal Remedies: Adverse Effects and Drug Interactions. American Academy of Family Physicians, March 1, 1999. 1239-47
  6. Eisenberg, M. David, MD. Advising patients who seek alternative medical therapies. Annals of Internal Medicine, Juy 1997; Vol 127 issue 1; 61-69.
  7. Williams, M. Cynthia, CAPT, MC, USN, Using Medications Appropriately in Older Adults. American Family Physician, November 2002; Vol 66, no 10; 1917-1924.
  8. Valli, Georginanne, MD, Giardina, V. Elsa-Grace, MD, FACC. Benefits, adverse effects and drug interactions of herbal therapies with cardiovascular effects. J. American College of Cardiology, 2002; Vol. 39, No. 7, 1083-1095.
  9. Natural Medicines Comprehensive Database. Consumer Information and Education.
  10. Bonakdar, A. Robert, MD. Herb-drug interactions: What physicians need to know. Patient Care Archive. January 2003, 1-13.
  11. Lambrecht, E. Jason, Pharm.D. et al. Review of Herb-Drug interactions: Documented and Theoretical. U.S. Pharmacist 25, no. 8, (2000):42.
  12. Chen, John, Pharm.D, Recognition and Prevention of herb-Drug Interaction.

Additional Resources

Steyer E. Terrence, MD. CAM: a Primer. Family Practice Management. March 2001,37-42.

Abele W. PhD. Herbal medication: Potential for adverse interactions with analgesic drugs. Journal of Clinical Pharmacy and Therapeutics. 2002, 27:391-401.S

tedman, Catherine, MB.ChB, FRACP. Herbal Hepatotoxity. Seminars in Liver disease/Vol 22, No 2, 2002, 195-206.