How does drug use lead to addiction?

Drug abuse, normally leads to addiction because of its attack on the brain. Your brain then becomes familiar to the feeling the drug brings when you've misused it. So when you try to stop, and you have symptoms of withdrawl, you often times feel the pain, and illness it brings, and then it becomes a choice whether to suffer through a couple of days or to keep using. When people make this decision it often leads to addiction to the the fact that your body is used to it. easy-peasy.