Relative imbalance in the number of drug-responsive modules, and numbers of genes within those modules, between cocaine and alcohol abuse may be due in part to the more restricted pharmacological effects of cocaine on dopaminergic processes through competitive inhibition of the dopamine transporter (Ritz et al., 1987); however, the pharmacological effects of alcohol are exerted by a wide-array of molecular mechanisms (Harris et al., 2008; Ron and Messing, 2013). The gene discussed is SLC6A3; the disease is alcohol abuse.