Colorado’s legalization of medicinal marijuana is linked to a rise in marijuana-related arrests in some parts of Nebraska.

Marijuana has now been legal in Colorado for medicinal use for more than 15 years. Over this time, authorities in neighboring Nebraska (where the drug remains illegal) have become concerned about the potential spillover of marijuana into their state’s counties. In new research, Jared M. Ellison and Ryan E. Spohn find that Nebraska’s border counties, and to a lesser extent those along the I-80 highway corridor, have experienced an upward trend in marijuana-related arrests and jail admissions. In light of these findings, they write, both states and the federal government may need to rethink their marijuana laws and make decisions about penalties and potential legalization.