There are a significant number of reports out there regarding youth usage. I am not exactly sure of the one you referenced, but I have seen reports that estimated an increase of approximately 20% at the onset. I saw a report a week ago indicating that youth usage has now stabilized and is slightly below the national average in the United States. There was at the onset a public education message to youth about the dangers of cannabis use for adults and youth. Our indication was that initially usage went up.
On September 12th, 2017. See this statement in context.