While most cannabis use studies focus on the effects of the long term use of the recreational drug, a recent study from Swinburne University in Melbourne has looked at the way one or two uses of cannabis can affect the way teenage brains develop. The research has uncovered that even after a single use of marijuana, teenagers had a larger amount of grey matter in their brain than those who had never used the drug. To explain the findings we were joined on the Daily by an author of this study, Dr Catherine Orr.