Drug addiction is a chronically relapsing mental illness involving severe motivational disturbances and loss of behavioral control leading to personal dev- tation. The disorder af?icts millions of people, often co-occurring with other mental illnesses with enormous social and economic costs to society. Several decades of research have established that drugs of abuse hijack the brain's natural reward substrates, and that chronic drug use causes aberrant alterations in these rewa- processing systems. Such aberrations may be demonstrated at the cellular, neu- transmitter, and regional levels of...