One of the reasons that appears in this world is the high number of relapses among people who currently use drugs or the very fact that these drugs do not affect not all users the same way. The model focuses on how drug-related cues trigger excessive drug motivation, leading to compulsive drug seeking (Vanderschuren & Everitt, 2004), drug use, and relapse (Robinson & Berridge , 1993). Simply put, repeated use and exposure to drugs sensitizes the affected pathways and neurons to tolerance, implying a decrease in drug effect with repeated administration. Furthermore, incentive sensitization theory provides us with evidence that a major reorganization of brain reward systems is possible, as people can develop chemical dependence upon drug exposure. New users are more likely to have a higher risk of becoming addicted based on their first encounter with the drug. For example, once an individual uses their first dose of heroin, each "high" will no longer be the same as the initial "high", leading to an increase in dose later on..