PHARMACOKINETIC AND PHARMACODYNAMIC HERB–DRUG INTERACTIONS: MECHANISM AND CLINICAL SIGNIFICANCE

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Abstract

The use of herbal medicines has grown rapidly across the world, both as complementary therapies and in combination with conventional medicines. As a result, the possibility of clinically important herb–drug interactions has become an increasing concern. Although herbal products are often considered safe because they are derived from natural sources, they contain biologically active compounds that can influence the effectiveness and safety of prescription medications. These interactions may occur through pharmacokinetic or pharmacodynamic mechanisms. Pharmacokinetic interactions involve changes in the absorption, distribution, metabolism, or excretion of drugs, commonly through the modulation of cytochrome P450 (CYP450) enzymes and drug transporters such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and organic anion transporting polypeptides (OATPs). In contrast, pharmacodynamic interactions occur when herbal constituents alter the pharmacological response of a drug by producing additive, synergistic, antagonistic, or toxic effects without necessarily affecting drug concentrations. Such interactions may reduce therapeutic efficacy, increase toxicity, or lead to serious adverse clinical outcomes. Clinically significant interactions have been documented with commonly used herbal products, including Hypericum perforatum (St. John’s wort), Ginkgo biloba, Allium sativum (garlic), green tea, grapefruit, valerian, chamomile, fenugreek, and licorice, particularly when used alongside anticoagulants, cardiovascular medications, central nervous system drugs, antidiabetic agents, immunosuppressants, and anticancer therapies. This review discusses the major pharmacokinetic and pharmacodynamic mechanisms responsible for herb–drug interactions, presents representative examples of clinical relevance, and examines their implications for patient safety. Greater awareness among healthcare professionals, routine documentation of herbal medicine use, stronger pharmacovigilance and herbovigilance practices, and well-designed clinical research are essential to reduce interaction-related risks and promote the safe integration of herbal medicines into modern healthcare.