Only associations with two genes, CNR1 (cannabinoid receptor 1, brain) and CHRNA5 (cholinergic receptor, nicotinic, alpha 5, neuronal) have been replicated so far.11, 12, 13 Other studies have assessed hundreds of single-nucleotide polymorphisms (SNPs) in multiple genes within candidate systems, and two genome-wide association studies have been reported in cocaine dependence, identifying shared as well as specific associations in European Americans and in African American populations.14, 15, 16, 17. This evidence concerns the gene CHRNA5 and cocaine dependence.