Drug addiction is a chronic, relapsing disorder characterized by compulsion to seek and take drugs, loss of control over intake, and a negative emotional state upon drug withdrawal. It involves elements of impulsivity and compulsivity, forming a three-stage cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation (craving). Neuroimaging studies have identified specific brain circuits involved in these stages, with the ventral tegmental area and ventral striatum mediating the binge/intoxication stage, the extended amygdala involved in withdrawal/negative affect, and a distributed network involving the orbitofrontal cortex, dorsolateral prefrontal cortex, and insula in craving. Neuroplasticity in these structures, starting with changes in the mesolimbic dopamine system, leads to dysregulation of the prefrontal cortex, cingulate gyrus, and extended amygdala, contributing to addiction. The transition to addiction involves neuroplasticity in all stages, beginning with initial drug use in vulnerable individuals. The neurocircuitry of addiction is influenced by genetic, developmental, and environmental factors. The addiction cycle is driven by positive and negative reinforcement, with the initial stages dominated by positive reinforcement and later stages by negative reinforcement and automaticity. The three stages of addiction are interconnected, leading to the pathological state of addiction. The neurobiology of addiction is influenced by changes in motivation, opponent process, and incentive salience. Drugs of abuse usurp brain systems that direct animals to rewarding stimuli, leading to increased incentive salience and drug-seeking behavior. The incentive salience hypothesis suggests that drugs increase the value of drug-related stimuli, leading to compulsive drug-seeking. Behavioral sensitization, measured by increased locomotor responses to repeated drug administration, is a key aspect of the transition from drug use to addiction. Animal models of addiction have provided insights into the neurocircuitry of addiction. These models show that chronic drug exposure leads to neuroadaptations in the brain, including changes in the mesolimbic dopamine system, the nucleus accumbens, and the extended amygdala. These changes contribute to the motivational aspects of addiction, including withdrawal and craving. Human studies using imaging and neuropsychopharmacology have shown that addiction involves neuroadaptations in brain circuits that process reward, memory, executive function, and stress reactivity. These adaptations are influenced by genetic, developmental, and environmental factors. The three stages of addiction—binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation—are associated with specific brain regions and neurotransmitter systems. The transition from drug use to addiction involves changes in the mesolimbic dopamine system, the nucleus accumbens, and the extended amygdala, contributing to the chronic and relapsing nature of addiction.Drug addiction is a chronic, relapsing disorder characterized by compulsion to seek and take drugs, loss of control over intake, and a negative emotional state upon drug withdrawal. It involves elements of impulsivity and compulsivity, forming a three-stage cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation (craving). Neuroimaging studies have identified specific brain circuits involved in these stages, with the ventral tegmental area and ventral striatum mediating the binge/intoxication stage, the extended amygdala involved in withdrawal/negative affect, and a distributed network involving the orbitofrontal cortex, dorsolateral prefrontal cortex, and insula in craving. Neuroplasticity in these structures, starting with changes in the mesolimbic dopamine system, leads to dysregulation of the prefrontal cortex, cingulate gyrus, and extended amygdala, contributing to addiction. The transition to addiction involves neuroplasticity in all stages, beginning with initial drug use in vulnerable individuals. The neurocircuitry of addiction is influenced by genetic, developmental, and environmental factors. The addiction cycle is driven by positive and negative reinforcement, with the initial stages dominated by positive reinforcement and later stages by negative reinforcement and automaticity. The three stages of addiction are interconnected, leading to the pathological state of addiction. The neurobiology of addiction is influenced by changes in motivation, opponent process, and incentive salience. Drugs of abuse usurp brain systems that direct animals to rewarding stimuli, leading to increased incentive salience and drug-seeking behavior. The incentive salience hypothesis suggests that drugs increase the value of drug-related stimuli, leading to compulsive drug-seeking. Behavioral sensitization, measured by increased locomotor responses to repeated drug administration, is a key aspect of the transition from drug use to addiction. Animal models of addiction have provided insights into the neurocircuitry of addiction. These models show that chronic drug exposure leads to neuroadaptations in the brain, including changes in the mesolimbic dopamine system, the nucleus accumbens, and the extended amygdala. These changes contribute to the motivational aspects of addiction, including withdrawal and craving. Human studies using imaging and neuropsychopharmacology have shown that addiction involves neuroadaptations in brain circuits that process reward, memory, executive function, and stress reactivity. These adaptations are influenced by genetic, developmental, and environmental factors. The three stages of addiction—binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation—are associated with specific brain regions and neurotransmitter systems. The transition from drug use to addiction involves changes in the mesolimbic dopamine system, the nucleus accumbens, and the extended amygdala, contributing to the chronic and relapsing nature of addiction.