This paper analyses scientific and grey literature that examines the consequences of drug law changes, and describes their approach and methodologies. A multi-part search strategy identified 36 primary studies coming from Europe, North America and Australia, which were then categorised by the type of legal change they examined; changes to laws addressing illegal use and possession, changes in laws regulating legal use and possession, and enforcement strategies of existing laws such as police crackdowns and employee drug testing. Across these studies, the authors identify five types of evaluation questions and indicators, three types of data sets, and two study designs that have been used. Evaluations may highlight the intended and unintended effects of a legal change, but there can also be unexpected effects, and the full picture will describe not only the unintended but also the unexpected effects. Evaluations should not be taken as black and white proof that one law is better than another; an objective and authoritative study result will be obtained by good design, questions and indicators that reflect a wide variety of concerns, and appropriate data sets. Such studies can be solid grounds on which policymakers can base their decisions on future changes.