An elderly patient with a mechanical heart valve experienced severe bleeding complications after combining warfarin, a blood thinner, with the Chinese herbal remedy danshen, commonly promoted for improving blood circulation. The case was handled by Dr. Raymond Wong Siu-ming, a consultant at the Prince of Wales Hospital’s Poison Treatment Centre and a lead expert at the Integrated Chinese-Western Medicine Treatment Safety Centre, highlighting the growing concern over potential interactions between traditional Chinese medicine (TCM) and Western pharmaceuticals.
In Hong Kong, Chinese medicine forms a routine part of many people's healthcare, encompassing practices such as drinking herbal teas, consuming tonic soups, and using proprietary herbal products. However, experts caution that natural origin does not guarantee safety, especially when concentrated herbal remedies are combined with conventional medications. Dr. Phoebe Zhou, senior research fellow at the NICM Health Research Institute in Australia, emphasized that the risk depends on the product's ingredients, dosage, duration of use, and individual patient factors such as liver or kidney function.
Potential interactions have been identified across various treatment areas including diabetes, cancer, infection, and inflammatory conditions. While many documented cases stem from laboratory or animal studies whose relevance to humans may vary, the need for caution remains significant, especially for individuals on multiple medications. Western supplements can also alter drug metabolism; for example, St. John’s wort can accelerate liver enzymes, reducing the effectiveness of birth control pills, blood thinners, and medications for depression or organ transplantation.
Danshen, or red sage—widely used in TCM for cardiovascular health—has been shown to increase warfarin’s blood-thinning effect in some clinical reports, a combination regarded as moderate risk by the Hospital Authority. Dr. Wong advises avoiding this pairing when possible; if co-administration is necessary, frequent blood-clotting tests are recommended. Conversely, ginseng may reduce warfarin’s efficacy, posing risks of insufficient anticoagulation and clot formation. Similarly, concurrent use of aspirin and danshen may nearly double anticoagulant effects and enhance bleeding risk, based on experimental research.
External TCM therapies also carry risks. Acupuncture, while generally low-risk, can cause localized bleeding or bruising in patients on anticoagulants, and certain points are contraindicated in pregnancy. Electroacupuncture may interfere with cardiac pacemakers, and cupping can rupture capillaries, posing concerns for individuals with fragile skin or bleeding disorders.
The Hospital Authority has evaluated 336 Chinese medicines used within its integrated Chinese-Western medicine program, identifying around 9 percent with documented interactions with Western drugs. To aid clinical decision-making, a four-tier risk classification system—high, moderate, low, and no reported risks—is employed, along with specific recommendations covering 90 herb-drug interaction pairs.
Healthcare professionals advise patients to fully disclose all medications, herbs, and supplements to all practitioners involved in their care. Carrying detailed information about herbal products, including ingredients, dosage, and timing, facilitates accurate assessment of any adverse effects or interactions. Immediate medical consultation is urged if new symptoms such as bleeding, dizziness, rash, palpitations, breathlessness, or signs of hypoglycemia develop after initiating an herbal remedy.
Experts underscore that combining traditional Chinese and Western medicines is not inherently unsafe but should be managed carefully and not improvised. As Dr. Lau Tang Ching, senior consultant in rheumatology and allergy at National University Hospital in Singapore, noted, "Tell both of your doctors everything. They cannot protect you from dangerous interactions if they only see half of the picture."