All procedures were performed in accordance with the Declaration of Helsinki. Data sets from the working group were selected that assessed individuals for dependence on one of five substances: alcohol, nicotine, cocaine, metham-phetamine, and cannabis. A variety of diagnostic instruments were used to assess substance dependence (see Table S1 in the online supplement). Case and control data were gathered from 23 laboratories on 3,240 individuals, of whom 2,140 were diagnosed with current dependence on at least one of the five substances of interest. Individuals were excluded if they had a lifetime history of neurological disease, a current DSM-IV axis I diagnosis other than depressive and anxiety disorders, or any contraindication for MRI. Control subjects may have used addictive substances recreationally but were not diagnosed as dependent. Summary demographic statistics (sex distribution and mean age) on participants whose data passed the quality control steps described below are provided in Table 1. Site-specific summaries are provided in Table S1 in the online supplement.
