Many people do not understand why or how other people become dependent on drugs. It is often mistakenly assumed that drug users lack moral principles or willpower and that they could stop using drugs simply by choosing to change their behavior. In reality, drug addiction is a complex disease, and quitting takes more than good intentions or a strong will. In fact, because drugs change the brain in ways that foster compulsive drug abuse, quitting is difficult, even for those who are ready to do so. We know that drug addiction can be successfully treated to help people stop abusing drugs and lead productive lives.