An Addiction Science Network Resource
The term addiction generally refers to the situation where drug procurement and administration appear to govern the individual's behavior, and where the substance seems to dominate the individual's motivational hierarchy. Two features that distinguish addiction from other behaviors are its extreme motivational strength and its motivational toxicity. Motivational strength refers to how hard the individual will work to obtain the substance, while motivational toxicity describes the substance's ability to disrupt the individual's normal motivations. This latter characteristic is particularly interesting because it may serve as a defining characteristic of addiction.
The individual is normally motivated to engage in a variety of behaviors. The relative importance of these rewards can be ranked to form a motivational hierarchy. Some motives will rank high, being extremely influential in the individual's behavior, while others will rank low, being relatively unimportant. The relative positions of motives on this hierarchy will vary from individual-to-individual as do what motives are even included on the list. Certain motivations are shared by all mammals (e.g., food, water, sexual behavior), while others appear unique to humans (e.g., career, television viewing).
Addictive substances have the ability to disrupt this motivational hierarchy. They do this in two ways. First, they can rapidly displace other motives in the individual's life, thrusting themselves to the top of the motivational hierarchy. Second, they can disrupt the ability of other, natural rewards to motivate behavior. The drug addict characteristically places substance use as their top priority, while losing interest in life's other rewards (e.g., food, sex). The intense desire to experience the effects of the addictive substance combined with the inability of natural rewards to engage behavior is subjectively experienced as a "loss of control." This perception, in a sense, is correct: the normal controls on the individual's life have lost their significance and behavior focuses on procurement and self-administration of the addictive substance.