Drug adsorption designates the accumulation of drug molecules at the interface between a fluid phase and a solid surface, driven by energetically favourable interactions that cause the solute to partition preferentially to the interface rather than remain in the bulk medium. The process is governed by the balance of forces between the drug, the solvent, and the solid adsorbent, and is operationally classified by the strength and nature of the surface interaction: physisorption involves weak, reversible forces such as van der Waals interactions and hydrogen bonding and typically permits multilayer formation, whereas chemisorption proceeds through covalent bonding, is often irreversible, and is restricted to a monolayer ^[1]. Within drug solubility and delivery systems, drug adsorption is a decisive determinant of formulation performance, because the extent and strength of drug binding to carrier surfaces such as mesoporous silica directly control drug loading, the completeness of release, and the achievable supersaturation of poorly soluble compounds ^[2][3]. The interaction is sensitive to the ionization states of both the drug and the surface, so that pH-dependent electrostatic attraction or repulsion modulates adsorption strength and, consequently, release behaviour ^[2]. The term therefore denotes the interfacial partitioning of a drug onto a solid substrate, together with the thermodynamic and kinetic parameters—isotherm models, binding affinity, and surface coverage—that quantify and predict this behaviour in pharmaceutical systems ^[3][4].