I'm not a fan of the Conservatives, and I think that we really need more impartial science around marijuana, but my understanding is that the stuff *does* adversely affect the growing brain. As such, I'm not sure what to make of this.
That said, I'm not sure whether my understanding is coloured by politically motivated science.
Either way, I'm sure that the campaign won't make a difference in the use of marijuana by teens. Very few things do.