Understanding and learning from the diversification of cannabis supply laws.

Background and aims Prohibitions on producing, distributing and selling cannabis are loosening in various jurisdictions around the world. This paper describes the diversification of cannabis supply laws and discusses the challenges to and opportunities for learning from these changes. Methods We document changes in cannabis supply laws that de jure legalized cannabis production for medical and/or non-medical purposes (excluding industrial hemp) in Australasia, Europe, North America and South America. We also highlight challenges to evaluating these legal changes based on our experiences studying cannabis laws and policies in the United States. Findings As of August 2016, two countries have passed laws to legalize large-scale cannabis production for non-medical purposes at the national (Uruguay) or subnational level (four US states). At least nine other countries legally allow (or will soon allow) cannabis to be supplied for medicinal purposes. Most of the changes in cannabis supply laws have occurred since 2010. The data available in most countries are inadequate for rigorously evaluating the changes in cannabis supply laws. Conclusion The evidence base for assessing changes in cannabis supply laws remains weak. Efforts should focus upon collecting information about quantities consumed and market transactions as well as validating self-report surveys. [ABSTRACT FROM AUTHOR]