Cannabis use jumps 20% in states after legalizing weed, new study suggests

A new study published in the journal Addiction has found a higher rate of cannabis use in states that have legalized the drug, comparing 111 pairs of twins split between states with and without legal cannabis.

“There appears to be a ~ 20% average increase in cannabis use frequency attributable to recreational legalization,” the study’s abstract stated.

The study used cohorts of twins from Colorado and Minnesota. While Colorado has legal weed and Minnesota does not, the two states are demographically similar.

“Observing differences within twin pairs provides a natural way to control potential confounding factors… twins provide extremely well-matched controls for each other,” the study’s introduction says.

Study co-author John Hewitt of the University of Colorado-Boulder said in a university press release, “This is the first study to confirm that the association between legal cannabis and increased use holds within families in genetically identical individuals.”

Although the study found that legalization increased cannabis use, the increase did not come from new users.

“Cannabis legalization may cause increased likelihood of recent use, but cannabis legalization is unlikely to cause initiation in individuals who were lifetime abstainers prior to legalization,” the study said.

Adults also have kept using cannabis, whereas in the past their use may have declined with the onset of life responsibilities.

“Typically, what we would expect to see is that people tend to increase use as adolescents and then reduce it as they transition into adult roles, family life and stable jobs. Interestingly, we saw escalation, not reduction, in adults,” study lead author Stephanie Zellers said in the CU-Boulder press release.