Evaluating the effect of retail marijuana legalization on parent marijuana use frequency and norms in U.S. States with retail marijuana legalization

•After 2012, marijuana use has increased among parents in RML and non-RML states.•Increased marijuana use is largely due to new users, both in RML and non-RML states.•Few differences in changes in marijuana use by gender, race/ethnicity, or education.•Pro-marijuana use norms have increased during that time period as well.•Norms have increased at a higher rate in RML states, compared to non-RML states. To examine post-retail marijuana legalization (RML) change in marijuana use frequency and pro-marijuana norms among parents. The Intergenerational Study, a longitudinal panel of parents (N = 668) and children, followed participants from 2002 to 2018, when parents were 27 and 43 years old, respectively. Three quarters of participants (74%) lived in an RML state and 142 (21%) had used marijuana in the 8 years prior to RML. Piecewise growth modelling compared pre- and post-RML slopes of use frequency and pro-marijuana norms. Frequency of use and pro-marijuana norms increased following legalization in both RML and non-RML states, though norms rose significantly faster in RML states. Growth in use was primarily driven by new users of marijuana. There were no differences in frequency of marijuana use or pro-marijuana norms by race/ethnicity, gender, or education. An increase in marijuana use frequency associated with RML among parents poses risk to both parents' well-being and the health of their children. A faster pace of increase in pro-marijuana norms in RML states may signal continued increases in use in the future.