Now let’s see what happens when we put cocaine into that system. In go the vesicles of dopamine, they travel to the receptor site, turn around and come back to the re-uptake site but cocaine has blocked it. [Just as Prozac, Zoloft or Paxil will block the re-uptake of serotonin]. When cocaine blocks re-uptake, the dopamine level goes sky high. This is stimulating, so we feel good: we're making great time, we don't know where we're going but we're really ahead of schedule! Next, the brain goes through what, in addiction medicine, we call a resetting. You may know it as tolerance.
Firstly, within milliseconds, the dopamine receptor sites are decreased by anywhere between 30% and 50%. Efferent neurons swell to a certain extent and there's not so easy a transduction of the impulse. Then a side chain called 3-Methoxytyramine detoxifies the dopamine, so the end result of that dopamine surge is a dopamine recession. The addict then takes more cocaine to get another dopamine surge but this results in further dopamine depletion, and so on.
Thus cocaine addiction is the seeking of pleasure and the avoidance of pain with complete disregard for the consequences (the chemical resetting of the brain).