Virtually all studies of policy diffusion are based on statutory enactments by state legislatures. But a substantial number of medicalized marijuana laws were initiated through citizen initiatives and ratified by referenda (I&R). This case study suggests that the diffusion of laws adopted by I&R requires two modifications to the conventional model of policy diffusion. First, early policy adoptions must occur through direct democracy so that horizontal diffusion results when those past adoptions by the I&R process lead to future adoptions. Second, the necessity of bypassing institutions of representative government must be operationalized as an interaction between the availability of direct democracy and the precise political variable that blocks legislative enactments.