SEATTLE – A new study says teen marijuana use appears to have dropped in Washington after the state legalized adult use of the drug in 2012.

The research, by the RAND Corp. and other organizations, said cannabis use fell by a small but statistically significant amount for eight- and 10th-graders in Washington, while use rates among high school seniors remained flat.

The findings were based on data from the Washington Healthy Youth Survey, conducted every two years.

They said marijuana use rates generally fell among Washington adolescents during 2014 and 2016 as compared to 2010 and 2012. For eighth-graders, marijuana use fell from 9.8 percent to 7.3 percent. Among 10th graders, use fell from 19.8 percent to 17.8 percent.

Researchers say that while the results are encouraging, more data is needed to evaluate how legalization affects teen use rates over the long term.