What is defined as the physical or psychological need for a drug to function normally?

The correct choice is defined as dependency. Dependency refers to a state in which an individual requires a substance, such as a drug, to maintain normal physiological or psychological functioning. This reliance often manifests as a physical need, where the absence of the drug can lead to withdrawal symptoms, or a psychological need, experienced as cravings or an inability to feel normal without the substance.

Dependency typically develops through prolonged use of a drug, which can alter the body's normal processes. For instance, the body may become accustomed to the drug's presence, leading to changes in brain chemistry that create a need for the substance to achieve a state of equilibrium.

In contrast, tolerance is the phenomenon where an individual needs an increased amount of the drug to achieve the same effect that was initially experienced with a smaller dosage. This does not denote the need for the drug to function normally; rather, it indicates a reduced responsiveness due to prior exposure.

Addiction is often a broader term encompassing both physical and psychological dependence, as well as the compulsive behavior surrounding drug use despite negative consequences. While it overlaps with dependency, it includes behavioral aspects that are not strictly related to the physical or psychological need for the drug to function normally.

Interference typically relates to disruptions caused by substance use on an individual's