Proposed in a 1975 Science journal study, the gateway theory suggests that using soft substances like cannabis, alcohol and tobacco is a behavioral doorway that leads to so-called hard drugs like heroin, cocaine, crystal meth and MDMA. The hypothesis—in effect an updated version of the 1930s stepping-stone theory—based its findings on observational data that says many hard-drug users previously smoked cannabis. Many question this approach because, using the same clinical standards, a researcher might observe the last three U.S. Presidents and conclude the plant is really a gateway to the White House. So is cannabis a gateway drug? In some ways, yes, but it is not exactly a gateway in the manner that prohibitionists suggest.