Has the U.S. reached the “tipping point” in marijuana legalization? That’s what one CNN commentator said happened last month when, on June 26, Oklahoma adopted medical marijuana through a ballot initiative — making it the 30th state to do so, as you can see in the figure below.
It’s true that a lot was unusual about the Oklahoma initiative. The state approved medical marijuana with roughly 57 percent of the vote — despite the fact that the ballot measure was held in a conservative state, during a primary — when only the most committed party members tend to vote — rather than during a general election, is more permissive than many comparable laws, and was opposed by statewide Republican leaders.
So was Oklahoma’s new law indeed a tipping point? Research on policy diffusion suggests that as neighboring states, provinces, or countries adopt a policy, the pressure for adoption increases among lagging jurisdictions. And in addition to the many states, the nation’s northern neighbor Canada legalized recreational use nationwide on June 19.