In spite of the variability of public policy toward drugs, relatively little attention has been devoted to providing positive explanations of drug legislation or to identifying economic interests which have benefited from such restrictions. With their general aim being to consider the motivating factors behind variability in drug policy, the authors estimate econometric models of U.S. senatorial support for prohibition in 1917 and for repeal in 1933. Their results indicate that while the commonly cited influence of public opinion clearly mattered, the systematic influence of the brewing/distilling industries and possibly underground suppliers can be detected in these votes.