The process of drugs moving across cell membranes is termed drug diffusion or transcellular transport. This process is essential for the absorption and distribution of medications within the body. Drugs can passively diffuse through cell membranes, often influenced by factors such as concentration gradients, membrane permeability, and the lipid solubility of the drug. Additionally, some drugs may utilize active transport mechanisms to cross membranes, requiring energy to move against the concentration gradient. Understanding these processes is vital for optimizing drug delivery and therapeutic efficacy.