As of midnight on Tuesday, the herb "qat" became a Class C drug. Users chew the leaves of this east African flowering plant to achieve a buzz which, some say, is similar to caffeine. The ban is surprising because the UK's Advisory Council on the Misuse of Drugs have argued that there isn't sufficient evidence that qat causes health problems to justify a ban. David Nutt is professor of neuropharmocology at Imperial College London and spoke to Chris Smith about the stimulant. Like this podcast? Please help us by supporting the Naked Scientists