Orange County News, April 11, 2007 Why does one person use drugs and become addicted while another doesn't? Why do addicts have trouble stopping drug use and staying clean and sober?  The answers to these questions are lodged in the brain. The brain sets the stage for an individual's sensitivity to the euphoric first effects of an abused drug and then it adapts with repeated exposure to that drug. The chronic, relapsing nature of addiction is caused by the brain changes that occur during this disease process.