Most teens report using marijuana less often after legalization. Only one group of teenagers used marijuana more often after retail sales were legalized in Washington than they did before -- high school seniors who work 11 or more hours per week, according to new research led by a WSU College of Nursing professor. Source 3z.
I'm assuming that when you give certain people independence over what they please in they tend to use it less knowing that they can get it at any time. However that's not the case if one of them has an addiction.