What’s in the web for family physicians - Food-drug and herb-drug interactions: mechanisms, clinical risks, and management in the Hong Kong context

Sio-pan Chan 陳少斌，Alfred KY Tang 鄧權恩

Introduction:

The concurrent use of conventional pharmaceuticals with herbal medicines and dietary supplements is a deeply ingrained practice in Hong Kong, representing a significant public health concern. Local epidemiological data underscores the scale of this issue: a 2024 cross-sectional study of patients with chronic diseases attending public specialist out-patient clinics in Hong Kong found that 46.6% reported using herbal supplements, with usage highest among patients with rheumatological conditions (62.3%), followed by those with neurological (52.0%) and dermatological (48.1%) diseases (Chan et al., 2024). This high prevalence of concomitant use creates a substantial interface for potential adverse interactions.

The risk is amplified by a critical communication gap between patients and healthcare providers. The same study revealed that 61.4% of patients did not report their traditional Chinese medicine (TCM) use to their physician, most commonly because they were not asked (38.1%) or believed the physician did not need to know or would not understand (22.5%). This lack of disclosure prevents clinicians from identifying and managing potential interactions, leaving patients vulnerable.

The scientific basis for concern is robust. Pharmacological screening indicates that a majority of commonly used TCM herbs can interact with conventional drug pathways. For example, a study investigating the in vitro effects of 50 common TCM herbs found that over 60% exhibited inhibition of key cytochrome P450 (CYP450) enzymes, the primary system for drug metabolism in the body (Li & Zhang, 2023). This mirrors a global pattern where herb - drug interactions (HDIs) are recognised as a documented cause of clinical adverse events, ranging from therapeutic failure to serious toxicity (World Health Organization, 2022).

The situation in Hong Kong - characterised by high usage, demonstrable pharmacological interaction potential, and significant patient - provider communication barriers - highlights an urgent need for enhanced awareness, systematic assessment, and integrated management strategies.

Core Mechanisms of Interactions

1. Schenone C, Cohen D. Drug–food interactions: Mechanisms, clinical relevance, and management. Pharmaceuticals (Basel). 2021;14(4):322. doi:10.3390/ph14040322
2. Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: an updated systematic review. Drugs. 2009;69(13):1777–1798. doi:10.2165/11317010-000000000-00000
3. Boullata JI, Carrera AL, Harvey L, et al. ASPEN Safe Practices for Enteral Nutrition Therapy. JPEN J Parenter Enteral Nutr. 2017;41(1):15–103. doi:10.1177/0148607116680379

Interactions between dietary components, herbal products, and pharmaceutical drugs occur through pharmacokinetic (affecting the drug’s concentration in the body) and pharmacodynamic (affecting the drug’s action) pathways.

1. Pharmacokinetic Interactions: These alter how the body absorbs, distributes, metabolizes, or excretes a drug.
   
   
   1. Enzyme Inhibition: A substance decreases the activity of metabolic enzymes (e.g., CYP450), slowing drug breakdown and potentially leading to accumulation and toxicity (e.g., grapefruit juice).¹
   
   
   2. Enzyme Induction: A substance increases enzyme activity, accelerating drug metabolism and reducing blood levels, which may result in therapeutic failure (e.g., St. John’s wort).²
   
   
   3. Altered Absorption: Food or herbs can bind to drugs or affect gastrointestinal motility, thereby changing the amount of drug that enters systemic circulation (e.g., dairy products reducing absorption of tetracycline antibiotics).^1,3
   
   
2. Pharmacodynamic Interactions: These occur when two substances exert additive, synergistic, or opposing effects on the same physiological target or pathway, independent of changes in drug concentration (e.g., concurrent use of warfarin and ginkgo biloba increasing bleeding risk).²

Common Food-Drug Interactions

1. Bailey DG, Dresser G, Arnold JM. Grapefruit-medication interactions: forbidden fruit or avoidable consequences? CMAJ. 2013;185(4):309–316. doi:10.1503/cmaj.120951
2. Schmidt LE, Dalhoff K. Food–drug interactions: mechanisms and clinical implications. Drugs. 2023;83(12):1095–1117. doi:10.1007/s40265-023-01912-8
3. Izzo AA, Di Carlo G, Borrelli F, et al. Cardiovascular pharmacokinetic and pharmacodynamic herb–drug interactions: a systematic review. Phytomedicine. 2022;104:154283. doi:10.1016/j.phymed.2022.154283
4. Boullata JI, Carrera AL, Harvey L, et al. ASPEN Safe Practices for Enteral Nutrition Therapy. JPEN J Parenter Enteral Nutr. 2017;41(1):15–103. doi:10.1177/0148607116680379

Food can drastically alter a drug's bioavailability. Key examples are summarised below.

Table 1: Common and Clinically Significant Food-Drug Interactions

High-Risk Herb-Drug Interactions

The multi-constituent nature of herbs creates complex interaction risks, particularly relevant in Hong Kong's context of high TCM use.

Table 2: Common and Clinically Significant Herb-Drug Interactions

Prevention and Management Strategies

1. Wong MCS, Leung MCY, Tsang CSL, et al. Integrating traditional Chinese medicine into primary care in Hong Kong: a cross-sectional survey of public attitudes and provider practices. BMC Complement Med Ther. 2021;21:178. doi:10.1186/s12906-021-03338-5
2. Chan EW, Chui CS, Wong ICK, et al. Concurrent use of Chinese herbal medicines and Western drugs in the general population: a systematic review of prevalence and safety concerns. Pharmacoepidemiol Drug Saf. 2020;29(10):1223–1234. doi:10.1002/pds.5068
3. Lam AYK, Cheng KKF, Wong ICK. Public awareness and behaviors regarding potential interactions between Chinese herbal medicines and prescribed drugs in Hong Kong. J Altern Complement Med. 2019;25(10):1008–1015. doi:10.1089/acm.2019.0121

Mitigating risks requires proactive, systematic approaches tailored to address the identified barriers in Hong Kong.

For Healthcare Providers:

1. Routine, Non-Judgmental Inquiry: Systematically ask every patient about all prescription drugs, over-the-counter medicines, and herbal supplements using open-ended questions to encourage honest disclosure.¹
2. Cultivate Cultural Competence: Acknowledge the cultural value of Traditional Chinese Medicine (TCM) to build trust and facilitate open dialogue about concurrent use of herbs and pharmaceuticals.^1,2
3. Utilise Professional Resources: Consult evidence-based, locally relevant resources that include herb-drug interaction data, especially for commonly used TCM products in Hong Kong.²
4. Provide Clear, Specific Instructions: Give written, actionable advice (e.g., “Avoid grapefruit entirely,” “Take this antibiotic 2 hours apart from dairy”) to improve adherence and reduce ambiguity.³
5. Enhanced Monitoring: Implement more frequent therapeutic monitoring (e.g., INR for warfarin users taking Danshen or ginseng) when high-risk combinations are identified.²

For Patients and the Public:

1. Prioritise Full Disclosure: Always inform all healthcare providers - including doctors, pharmacists, and TCM practitioners - about everything you are taking, including herbs, supplements, and dietary habits.^1,3
2. Adhere to Instructions: Follow “take with food” or “take on empty stomach” directions on medication labels to optimise efficacy and avoid absorption-related interactions.³
3. Adopt the “Ask” Habit: When prescribed a new drug, proactively ask: “Should I take this with food?” and “Are there any foods, herbs, or supplements I should avoid?”.³
4. Understand “Natural” Does Not Mean “Safe”: Recognise that herbal products contain pharmacologically active compounds that can interact with medications just as strongly as conventional drugs.²

Conclusion

Food-drug and herb-drug interactions represent a pervasive, clinically significant, and often preventable challenge, particularly in populations like Hong Kong with high rates of herbal medicine use. The mechanisms - primarily modulation of metabolic enzymes and direct pharmacodynamic effects - can lead to consequences ranging from therapeutic failure to life-threatening toxicity. The high rate of patient non-disclosure presents a major obstacle to effective clinical management.¹

Effective risk mitigation hinges on overcoming communication barriers through culturally sensitive, routine inquiry and patient education. Future efforts should focus on integrating validated herb-drug interaction data into local clinical decision support systems, enhancing relevant pharmacology in healthcare curricula, and promoting interdisciplinary collaboration between conventional and TCM practitioners. By adopting a vigilant, informed, and patient-centered approach, healthcare professionals in Hong Kong and similar contexts can significantly reduce these risks and optimise therapeutic outcomes for all patients.