What is defined as a mental or physical need to have a substance?

The correct choice is addiction, as it is characterized by a compulsive engagement in rewarding stimuli, despite adverse consequences. This term encompasses both mental and physical needs for a substance. Individuals with an addiction often experience cravings and a loss of control over their use of the substance, which can lead to significant impairment in daily functioning and overall quality of life.

Dependency, while related, typically refers to the physiological state where the body has adapted to a substance, causing withdrawal symptoms when the substance is not available. Tolerance involves the body's diminishing response to a substance after repeated use, requiring increased amounts to achieve the same effect. Intoxication describes the state of being under the influence of a substance, which does not inherently imply a chronic need or desire for continued use. Thus, addiction best captures the ongoing need for a substance, encompassing both mental and physical aspects.