Cannabis use when it's legal.

@article{Ours2007CannabisUW,
  title={Cannabis use when it's legal.},
  author={Jan van Ours},
  journal={Addictive behaviors},
  year={2007},
  volume={32 7},
  pages={1441-50}
}
This paper addresses the question of whether alcohol and tobacco are "gateways" for cannabis use. To investigate this the relationships between the starting rates in the use of alcohol, tobacco, and cannabis are analyzed. The starting rate for cannabis use appears to be higher for smokers and lower for users of alcohol. Indeed, tobacco use seems to be a gateway for cannabis use. The main policy conclusion is that measures that reduce smoking will also reduce the incidence of cannabis use.