In November last year the American state of Colorado voted to legalise the recreational use of cannabis. It is the most radical experiment in drugs policy for generations and the world will be looking to see what happens, particularly to drug use amongst teenagers. In this hour long documentary for This World, clinical psychologist and addiction expert Professor John Marsden heads to Denver, the state capital, to assess the likely impact of legalisation on a country already suffering an epidemic of teenage marijuana use.
