How addictive is cannabis? Does it lead to harder drug use, or is it an underappreciated herbal medicine? Can it cause mental illness? This program explores the science and the public debate surrounding the world’s favorite illegal drug. Tracing the birthplace of the humble plant to Kazakhstan in Central Asia, addiction specialist Dr. John Marsden guides viewers through several topics and issues—including links between THC and schizophrenia; experiments on mice suggesting cannabis-related cognitive impairment; the development of Sativex, a cannabis-derived medicine; and California’s medical dispensary system, which bears some resemblance to the legalization of marijuana. A BBC Production. (51 minutes)