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Chinese and Western Herbal Medicine: A Guide to Potential Risks and Drug Interactions

Author(s): Hue C. Thai, ND
Date Authored: September 01, 2004

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 article on EthnoMed:  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 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 paper 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 defects ) effects

Hirudo seu whitmania
Shui zhi
Moschus She xiang
Mulabris Ban 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 their potential for herb-drug interactions

Herbs Drug Interactions
Adverse potential
Bupleurum spp.
(Chinese Thoroughwax, Chai Hu)

  • Primary use: symptoms associated with common cold, flu, liver disorders…

  • Primary action: Bupleurum stimulates the immune system
  •  None Known







  •  Some side effects of this herb include increased bowel movement, and drowsiness.




Danshen (Salvia miltiorrhiza)

  • Primary usage: promotes blood flow and treat cardiovascular diseases i.e. angina pectoris, acute MI.

  • Primary actions: scavenges free radicals, inhibit platelets aggregration, and promote vasoactive.
  •  Warfarin








  •  Decreases warfarin clearance and increases its bioavailability. Case report of hemorrhage.






 Dong Quai
(Angelica Sinensis, Dong Gui, Chinese Angelica, Tan Kuei)

  • Primary use: It is most often used in oriental medicine for menstrual problems.

  • Dong Quai can also be widely found in traditional formulation for pain.




  •  Warfarin











  •  Dong Quai is safe for most adults. Women who are pregnant or breast-feeding should not take it without consulting their healthcare provider.

  • Women with hormone sensitive cancers such as breast, uterine, or ovarian cancer and those with endometriosis or uterine fibroids should also exercise caution.
Ephedra Sinensis
(Cao Mahuang, Ma huang, Yellow astringent)

  • Primary use: Ma huang is well known as a weight loss pill in the West (i.e. herbal fen-phen), but it is solely used in traditional oriental medicine for respiratory conditions such as asthma, bronchitis, and bronchospasm.













  •  MAOI, caffeine, decongestants, stimulants

  • People with the following condition should not take Ephreda: Chest pains, cardiovascular disease, anxiety, eating disorder, and thyroid problems.















  •  Ephedra and MAOI can cause dangerously high blood pressure. FDA proposed a dosage limit of 8 mg every 6 hours (or a total of 24 mg per day) and not more than 7 days of continuous use.
  • Ephedra, by itself, is not recommended for most people. It is never used alone in TCM.
  • Risks of prolonged usage and high dosages consumption include: high blood pressure, stroke, heart attacks, seizures, irregular heart beat, loss of consciousness, and death.
  • Less severe adverse symptoms include: dizziness, restlessness, anxiety, irritability, heart pounding, headache, a loss of appetite, nausea, and vomiting.
Feverfew (Tanacetum parthenium)

  • Primary use: migraine prophylaxis

  • Primary actions: vasoactive effects, anti-inflammatory, inhibit platelet aggregation
  • Antiplatelet drugs
  • Ticlopidine
  • Clonidine
  • Tricyclic antidepressants


  •  Potential antiplatelet effects
  • Antagonizes serotonin release, may potentiate the effects of other serotonin antagonists.


Garlic (Allium sativum)

  • Primary use: reduce low density (LDL) cholesterol, elevate high density (HDL) cholesterol, mildly reduce blood pressure, and improve blood circulation. Garlic is also been used as an antibacterial/antiviral (H. pylori).

  • Primary actions: inhibit platelet nitric-oxide-synthase, enhance fibrinolytic and antiplatelet activity, and antiviral & antibacterial activities.
  •  Garlic can INCREASE the risk for bleeding when combined with:    Warfarin, aspirin, clopidogrel (Plavix), and enoxaparin (Lenvenox).
  • Garlic may DECREASE the effectiveness of: cyclosporine, and BCP.





  •  Garlic is generally safe for most adults.
  • Raw garlic can cause: a burning sensation in the mouth or stomach, heartburn, bad-breath, gas, nausea, vomiting, and diarrhea.






Ginger (zingiberis rhizome)

  • Primary Use: a spice, ginger is used for sea-sick and motion sickness, and loss of appetite



  •  Increase risk of bleeding when combined with blood thinners such as warfarin, and aspirin.
  • Ginger may interfere with medications for controlling blood sugar, blood pressure, and stomach acid.
  •  Most people tolerate ginger well.






Ginseng (Panax species)

  • Primary use: vigor, well-being and longevity, MI, angina pectoris, CHF, lowering blood sugar.

  • Primary action: It is thought that ginseng contains a variety of chemicals called ginsenosides that are responsible for its effects. In herbal therapy, Ginseng is often used as an adaptogenic herb, which means that it can regulate a hypo or hyper functioning system.
  •  Warfarin
  • Alcohol
  • Phenelzine; MAOI









  •  Decreased INR
  • Increased alcohol clearance
  • headache, tremor, mania









Hawthorn (Crataegus oxyacantha)
  • Primary use: Hawthorn is often prescribed for cardiovascular problems including heart failure.

  • Primary action: increase cardiac output, increase nerve signal transmission, and relax blood vessels.
  •  Hawthorne may increase the effects of cardiovascular medication such as:
  • Digoxin, enalapril, metoprolol, nitroglycerin, propranolol, Theophylline, caffeine, papverine.


  •  Hawthorn is safe for most people. Occasional reactions to Hawthorn include: nausea, stomach upset, fatique, sweating, headache, and dizzines




Kava kava
(Piper methysticum)

  • Primary use: sedative, anxiety, reducing withdrawal symptoms from benzodiazepines.

  • Kava-lactones are believed to affect the central nervous system.


















  • Kava can INCREASE SIDE EFFECTS of the following drugs: alcohol, sedatives, sleeping pills, and antipsychotics.

-diazepam (Valium),   
-alprazolam (Xanax),
-Halcion, Phenobarbital

  • Kava may INCREASE RISKS of liver damage when combined with a number of medications: acarbose, amiodarone, atorvastatin, diclofenac, isoniazid, itraconazole, ketoconazole, leflunomide, lovastatin, methotrexate, nevirapine, niacin, nifampin, ritonavir, simvastatin, tacrine, tamoxifen, terbinafine, valproic acid, zileuton…

  • Kava can INCREASE the risk of abnormal muscle movements when combined with certain meds: chlorpromazine, fluphenazine, haloperidol, metoclopramide, thioridazine, and thiothixene.
  • Kava can DECREASE the effectiveness of dopamine.
  •  The potential for herb-drug interaction is much greater when Kava is combined with western drugs. One should not take Kava while one is pregnant or breastfeeding, depressed, or have liver disease such as hepatitis.


















(Glycyrrhiza glaba)

  • Licorice is a very popular herb in TCM formulations, often used to ameliorate or neutralize potentially toxic herbs.









  •  Licorice DECREASE high blood pressure medications such as: procardia, cardizem, tenormin, lasix. In addition, it also decrease the effects of hormone therapies i.e. estrogen, tamoxifen, birth control pills.
  • Licorice INCREASE the side effects of prednisone, and other steroid medications, MAOI, insulin, ibuprofen, naproxen, lovastatin ketoconazole, Allegra, Halcion, Seconal, and other drugs that are metabolized by CYP450.
  •  High dosage or long-term use of licorice can lead to high blood pressure, water and sodium retention, and decreased potassium in the blood.
  • Potassium depleting drugs such as furosemide, ethacrynic acid, grape fruit juice, and laxatives can increase the side effects of licorice.





 Senna, cascara
  •  Possible interference with any intestinally absorbed drug
  •  Decreased drug availability
 St. John’s Wort
(Hypericum perforatum)

  • Primary use: mild-moderate depression, possibly effective for anxiety.
  • Primary actions: hyperforin and hypericin act on chemical receptors to regulate mood.
















  •  SJW can significantly decrease availability and absorption of many drugs by inducing liver enzyme CYP 450 and inhibiting, including drugs for:
• SSRI’s
• Anxiety
• Asthma
• Birth control (OCP)
• Cholesterol lowering
• Depression
• Heart
• Phenobarbital, dilantin, tegretol, Xanax.

  • SJW can increase side effects of many drugs, for example:
  • Allergy (Allerga)
  • Depression (Zoloft, MAOIs, Paxil, Serone)
  • Migraine (Imitrex, Frova, Amerge, Maxalt)
  • SJW has also been reported to interact with anesthesia. It is recommended that patients discontinue SJW two weeks prior to surgery.
  •  By far, SJW has been the most commonly reported herb causing herb/drug interactions. Short-term use appears to be safe for most consumers. In some patients, SJW can cause insomnia, restlessness, vivid dreams, anxiety, irritablility, stomach upset, fatigue, dry mouth, dizziness, headache, and tingling.
  • SJW can cause skin to become extra sensitive to the sun, especially in light-skinned individuals.









(sexual dysfunction)
  •  Tricyclic antidepressants
  •  Hypertension

(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 hot, warm, 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 on EthnoMed:  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.
  • Stedman, Catherine, MB.ChB, FRACP. Herbal Hepatotoxity. Seminars in Liver disease/Vol 22, No 2, 2002, 195-206.