In the United States, cannabis remains illegal at the federal level, but 24 states have a medical cannabis programme. Some have gone even further, such as Colorado, the first state to pass recreational cannabis laws. Ever since the changes came into effect in January 2014, business has been booming: 18,000 new jobs have been created and crime is falling. But easy access to cannabis also comes with its own share of problems, as our reporters found out.
Programme prepared by Patrick Lovett and Elise Duffau