Lawful Access to Cannabis: Gains, Losses and Design Criteria

"Legalisation" does not specify a policy. Cannabis could be made available for use by adults under a wide variety of conditions: cheap or expensive, offered by for-profit enterprises, by not-for-profits (including consumer co-operatives), as a state monopoly (for production or sales or both), or even on a "grow-your-own" basis. It could be cheap (as it would be in a free market) or expensive (due to taxes or minimum pricing). Marketing efforts could be free or restrained.  Users could be "nudged" toward temperate use - for example, through a system of user-set but enforceable periodic purchase limits - or left to their own devices. Policy-makers should keep in mind Pareto's Law, which applies to cannabis consumption: about four-fifths of consumption is accounted for by about one-fifth of consumers.  That fact will drive the commercial strategies of for-profit producers and sellers, and should focus the attention of public agencies on the risks and harms to the heavy-using minority. Uncertainties abound, and consequently policies should be designed to allow the system to learn from experience. But it is possible to try to predict and evaluate – albeit imperfectly – the  likely consequences of proposed policy changes and to use those predictions to choose systems of legal availability that would result in better, rather than worse, combinations of gain and loss from the change.