A Review on Effect of Herbs on Absorption, Distribution, Metabolism, Elimination of Therapeutic Drugs

Abstract

The use of herbal medicines has become increasingly widespread across the world, with a significant proportion of the population relying on herbal products either as primary therapeutic agents or as complementary treatments alongside conventional medicines. The growing popularity of herbal remedies is largely attributed to their accessibility, affordability, cultural acceptance, and the common perception that natural products are inherently safe. However, despite their therapeutic potential, herbal medicines contain numerous biologically active constituents capable of interacting with prescription and over-the-counter drugs. Such interactions can alter the pharmacokinetic profile of therapeutic agents and may result in clinically significant consequences. Pharmacokinetics encompasses four fundamental processes—absorption, distribution, metabolism, and elimination (ADME)—which collectively determine the concentration of a drug in the systemic circulation and at its site of action. Herbal products can influence these processes through various mechanisms, including modification of gastrointestinal physiology, alteration of plasma protein binding, regulation of drug transporters, modulation of hepatic and intestinal drug-metabolizing enzymes, and changes in renal excretion pathways. Among these mechanisms, the induction or inhibition of cytochrome P450 (CYP450) enzymes and membrane transport proteins such as P-glycoprotein has emerged as a major factor responsible for herb–drug interactions.
Several widely used herbal medicines, including Hypericumperforatum (St. John’s Wort), Ginkgo biloba, garlic (Allium sativum), ginseng (Panax ginseng), grapefruit (Citrus paradisi), cranberry (Vacciniummacrocarpon), licorice (Glycyrrhizaglabra), and milk thistle (Silybummarianum), have been reported to significantly alter drug absorption, tissue distribution, metabolic clearance, and elimination. These interactions may lead to decreased therapeutic efficacy, increased drug toxicity, adverse drug reactions, treatment failure, or serious clinical complications, particularly in patients receiving drugs with a narrow therapeutic index such as warfarin, cyclosporine, digoxin, tacrolimus, and certain anticancer agents. The increasing prevalence of poly-pharmacy, self-medication, and the concomitant use of herbal and conventional medicines has heightened concerns regarding the safety and effectiveness of pharmacotherapy. Furthermore, variability in herbal product composition, lack of standardization, and limited patient awareness often complicates the identification and management of herb–drug interactions. Therefore, understanding the influence of herbal medicines on drug disposition is of paramount importance for healthcare professionals, researchers, and regulatory authorities.
This review critically examines the current scientific evidence regarding the effects of herbal medicines on the absorption, distribution, metabolism, and elimination of therapeutic drugs. It discusses the molecular mechanisms underlying these interactions, summarizes clinically relevant herb–drug interaction studies, and highlights their implications for patient safety and therapeutic outcomes. The review also emphasizes the need for enhanced pharmacovigilance, standardized herbal formulations, and evidence-based clinical guidelines to ensure the safe and rational integration of herbal medicines into contemporary healthcare systems.

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