There are fears that if parents reveal their use, teens will be more likely to give it a try, a phenomenon supported by research. And although the science is fairly new, some studies have found heavy marijuana use in adolescence can permanently disrupt key networks in the developing brain associated with memory and processing information.

“For parents, this is a confusing time. If they’re users, how are they going to talk to their kids?” said Matthew Kuehlhorn, founder of Community Thrive, a new organization in Colorado that helps facilitate such talks in an effort to prevent youth substance use. “This is a social culture change we haven’t seen the likes of since alcohol prohibition ended.”

Kathy Henderson, who leads a Parents Against Pot effort in her Trinidad neighborhood in Northeast Washington, said she has noticed that legalization has led to a higher incidence of children “walking around the street openly smoking marijuana and thinking it’s okay.”