So hypothetically then, based on your numbers Woob.
Assume a controlled population of 10,000,000 (arbitrary number) regular teenagers.
7/1000 = .007 * 10MM = 70,000 people with a chance to manifest normally.
42/1000 = 0.042 * 10MM = 420,000 people with a chance to manifest using marijuana heavily.
This article discusses some of the costs and burdens placed on society in Canada of mental health issues:
http://strategy.mentalhealthcommissi...estment-en.pdf
There looks to be a few different numbers thrown around in that study of the various costs, but lets use a conservative estimate of $150,000 of incremental lifetime costs to the medical system.
Keep in mind this does not consider the additional burdens placed on families, friends, employers, etc.
420,000 - 70,000 = 350,000 incremental mental health issues experienced in the controlled population of 10,000,000.
350,000 * 150,000 = $52.5Bn in incremental costs.
Pretty interesting when $ values start to be assigned. Obviously this is very rudimentary, but the premise is valid.