No serious commentator doubts that cannabis is potentially damaging to the user. Like tobacco, it is typically smoked and thus shares the potential for lung disease. Like alcohol, it affects reaction times and may raise the risk of road accidents. Cannabis has also been associated with cognitive impairment, deterioration in education performance (van Ours and Williams 2008), and psychotic illness (Arsenault 2004). Moreover, cannabis is often – albeit contentiously – seen as a causal gateway to more serious drug use (Kandel 2002). The question is what to do about it?