What causes physical dependence on a drug?

Physical dependence on a drug is a condition that arises from physiological changes in the body due to the frequent use of that substance. When an individual uses a drug over an extended period, their body can adapt to the presence of the drug, leading to changes in neurochemical processes, receptor sensitivities, and the overall functioning of various systems. This physiological adaptation means that the body becomes reliant on the drug to maintain a normal state, and when the drug is not present, withdrawal symptoms can occur. Thus, the underlying cause of physical dependence is rooted in these biological and physiological changes that happen with consistent drug use.