For decades, the United States of America was seen as the post powerful supporter of the prohibitionist interpretation of the UN drug conventions and one strong promoter of the ‘‘war on drugs’’. Yet, in five years, eight states out of fifty have taken a step in the regulation of cannabis – legalizing cultivation, sale, possession and recreational use of marijuana for adults aged 21 or older under state law, despite the federal ban. Today, in the third most populous country in the world, 20  of the US population lives in a jurisdiction experiencing a new system of marijuana legal regulation. The legalization of ‘‘recreational’’ cannabis adds complexity to a contrasting situation where 29 out of 50 states (as well as Washington DC) already authorize the therapeutic use of cannabis. This paper examines the ongoing process in the states that have legalized the possession and sale of cannabis for recreational purposes since 2012, in order to identify the conditions for marijuana reform. It outlines the major background factors that may explain such legal evolutions, firstly the election of Barack Obama to the presidency of the United States in 2008. The analysis compares what we know about regulatory regimes now being introduced with significant disparities.