Outcome measures - Biological specimens from the addiction patients and controls will be used to derive and characterize patient-specific, induced pluripotent stem (iPS) cells that carry monoamine transporter polymorphisms. Patient-specific iPS cells lines will be differentiated into dopaminergic neurons. In follow up studies, we will characterize, compare, and functionally assay these patient-specific, iPS cell-derived dopaminergic neurons from control and addiction patients that carry polymorphisms for hDAT1 and hVMAT2 gene to investigate any possible association with dopamine neurotransmission variations and vulnerability to addiction.