By Molly Rosbach, OSU report. CORVALLIS, Ore. – Marijuana use among college students has been trending upward for years, but in states that have legalized recreational marijuana, use has jumped even higher. An Oregon State University study published in Addiction shows that in states where marijuana was legalized by 2018, both occasional and frequent use among college students has continued to rise beyond the first year of legalization, suggesting an ongoing trend rather than a brief period of experimentation. Overall, students in states with legal marijuana were 18% more likely to have used marijuana in the past 30 days than students in states that had not legalized the drug. They were also 17% more likely to have engaged in frequent use, defined as using marijuana on at least 20 of the past 30 days. The differences between states with and without legalization escalated over time: Six years after legalization in early-adopting states, students were 46% more likely to have used marijuana than their peers in non-legalized states.