Chemical standardization is central to the quality control of herbal medicines, yet reproducible constituent content does not necessarily produce reproducible systemic exposure. This translational review examines why that gap persists by integrating evidence on product matrix, co-constituent interactions, dose and administration, host physiology, metabolism, transport, microbiota, formulation, and bioanalytical measurement. The selected literature indicates that exposure is generated downstream of composition through a sequence of conditional processes: liberation from the dosage form, dissolution and stability, intestinal transformation, transporter and enzyme activity, microbial metabolism, first-pass disposition, tissue distribution, and analytical detection of parent compounds and metabolites. Human pharmacokinetic studies show that nominally similar or standardized botanical preparations can yield different exposure profiles, while formulation studies demonstrate that solubilization and delivery systems can modify absorption and distribution. Host-dependent evidence further implicates sex, genotype, physiological state, and microbiome composition or function, although the strength and translational proximity of these findings vary substantially. The review therefore proposes that chemical standardization and exposure standardization should be treated as related but non-equivalent objectives. A product may meet compositional specifications while remaining pharmacokinetically variable across formulations, regimens, or individuals. For development, the implication is not to abandon chemical markers, but to connect them with exposure-relevant testing when mechanistically and clinically justified. Major limitations include heterogeneous products, small human pharmacokinetic datasets, uneven metabolite coverage, species translation, and incomplete causal validation of microbiome and transporter mechanisms.
