E-Mail New research from the Prevention Research Center of the Pacific Institute for Research and Evaluation examines whether recreational marijuana legalization in Oregon and marijuana and alcohol retail outlet density levels are associated with co-use and beliefs supportive of use of each among teens. Using data from 11th graders who participated in the Student Wellness Survey from 2010-2018, researchers assessed past-30-day co-use changes in counties with low, medium, and high densities of licensed marijuana and alcohol outlets. Findings include: A significant post-legalization increase in past-30-day co-use in 2016 in counties with the highest retail outlet density. Significant post-legalization increases in perceived risk and parent approval of alcohol and marijuana use.