January 2015 marks 100 years since drugs were first banned. Johann Hari set off on a three-year long, 20,000-mile journey to find out why they were criminalised, how this is causing a disaster today and what happens when you choose a radically different path. His discoveries are told entirely through the startling and moving stories of real people - from a transsexual crack dealer in Brooklyn, to a Hungarian Holocaust survivor who discovered the real causes of addiction.