Addiction has been called a disease of learning. Once addicted, it is very difficult to unlearn the behavior. For drug addiction, the drugs themselves mimic or alter the ability of neurotransmitters to function properly and for synapses to remodel. A number of the materials on this website address this subject.
BrainU lesson plans on the subject of addiction
C. elegans and Alcohol is a laboratory experiment in which students test the effects of alcohol on the roundworm.