Herbal medicines remain important components of healthcare worldwide; however, their therapeutic application is often constrained by poor aqueous solubility, limited membrane permeability, extensive first-pass metabolism, chemical instability, and variability in composition, resulting in low and inconsistent bioavailability. Nanotechnology-based delivery systems offer a promising approach to address these limitations by improving the physicochemical and biopharmaceutical properties of plant-derived bioactive compounds. This review critically evaluates recent advances in the nanoformulation of herbal medicines, covering liposomes, phytosomes, polymeric and protein-based nanoparticles, solid lipid nanoparticles, nanocrystals, nanoemulsions, and green-synthesized metallic nanoparticles. Particular emphasis is placed on four representative phytoconstituents, curcumin, quercetin, silymarin, and resveratrol, through comparison of their conventional and nanoformulated forms in terms of physicochemical properties, pharmacokinetic behavior, therapeutic performance, and safety. Evidence from the reviewed studies indicates that nanoformulation can substantially enhance solubility, stability, bioavailability, controlled delivery, and target-site accumulation of phytoconstituents, with corresponding improvements in antioxidant, hepatoprotective, anticancer, and antimicrobial activities, particularly in preclinical models. Nevertheless, clinical translation remains hindered by insufficient long-term nanotoxicological data, variability in formulation and characterization methods, limited clinical evidence, manufacturing challenges, and the absence of harmonized regulatory frameworks. Overall, nanotechnology provides a promising platform for improving the delivery and therapeutic performance of herbal medicines; however, successful translation into clinically applicable products will require standardized physicochemical characterization, rigorous safety and efficacy evaluation, scalable manufacturing approaches, and clearly defined regulatory pathways.
