Abstract
It is presumed that 5.2 percent of the global population between the ages of 15 and 64 years used an illicit drug in 2014. Although dependence is accepted in the current classification International Classification of Diseases (ICD-10), owing to the physiological drug response, addiction, defined as compulsive drug-seeking and use, may be more applicable in other circumstances.
Regular consumption of drugs causes persistent changes in the brain structures (neuroadaptation) that explain the shift from voluntary drug use to non-voluntary, and therefore, compulsive drug use. Compulsive consumption behavior relies, in a psychologically way, the positive reinforcement due to the seeking pleasure and the continuous gratification in this matter. Positive reinforcement is associated with learning with his molecular biological mechanism - neuronal plasticity at the hippocampus.
The neurobiology of addiction consists in the three‐stage addiction cycle: binge/intoxication, preoccupation/anticipation and withdrawal/ negative affect. This is reinforced by multiple neuroadaptations in three conforming domains: (1) increased incentive salience, (2) decreased brain reward and increased stress, (3) compromised executive function; and in three chief neurocircuits: basal ganglia, extended amygdala, and prefrontal cortex.
There are a series of neurotransmitters and neuromodulators that are implicated in the complex mechanisms of addiction. Dopamine intervenes in the reward effects of the drugs and the conditioning and memory mechanisms resulting in drug cravings and compulsive drug. Negative reinforcement, the negative emotional state of withdrawal is intermediated by stress‐related neurotransmitters, particularly corticotropin‐releasing factor (CRF) and dynorphin. Norepinephrine systems in the extended amygdala act in the negative motivational state.

Key words: addiction, compulsive use, reinforcement