What has research over the past two decades revealed about the adverse health effects of recreational cannabis use?

To examine changes in the evidence on the adverse health effects of cannabis since 1993.A comparison of the evidence in 1993 with the evidence and interpretation of the same health outcomes in 2013.Research in the past 20 years has shown that driving while cannabis-impaired approximately doubles car crash risk and that around one in 10 regular cannabis users develop dependence. Regular cannabis use in adolescence approximately doubles the risks...