Many people mistakenly view drug abuse and addiction as strictly a social or personal problem and may characterize those who take drugs as morally weak. One very common belief is that drug abusers should be able to just stop taking drugs if they are only willing to change their behavior. Most people do not understand why individuals become addicted to drugs or how drugs change the brain to foster compulsive drug abuse. Drug addiction is a complex disease that impacts the brain and because of that, stopping drug abuse is not simply a matter of willpower. Through scientific advances, we now know much more about how exactly drugs work in the brain, and we also know that drug addiction can be successfully treated to help people stop abusing drugs and resume their productive lives.
(Adapted from: http://www.nida.nih.gov/infofacts/understand.html)