Meet Carl Hart: parent, Columbia professor — and heroin user

Have the dangers of recreational drug use been overstated? For Dr Carl Hart, a well regarded Ivy League professor and heroin user, they certainly have. In fact, he believes that in general, medicine's highly cautious approach to drugs has an "immense cost" to humanity — a fascinating argument that he explores further talking to Andrew Anthony, from the Guardian, ahead of the release of his startling new book "Drug Use for Grown-Ups".