addiction

Meaning: Addiction (substance use disorder) is compulsive seeking and use of a substance despite harmful consequences. Many drugs of abuse increase dopamine signaling in the mesolimbic reward pathway, from the ventral tegmental area to the nucleus accumbens. Repeated use causes tolerance (a larger dose is needed for the same effect) and, with many substances, withdrawal when use stops.

On the MCAT: Passages ask you to separate positive reinforcement (the high strengthens use) from negative reinforcement (taking the drug to end withdrawal discomfort strengthens use). Cues paired with the drug can trigger craving through classical conditioning. Questions may also use a biopsychosocial view, in which genetic vulnerability, stress, peer influence, and availability each raise risk.

Common confusion: Students treat addiction as the same thing as physical dependence. Tolerance and withdrawal can occur in a person taking a medication as directed, without compulsive use, so the defining feature is loss of control despite harm. Also, negative reinforcement is not punishment: it removes an unpleasant stimulus and increases the behavior.