How ideology shapes the evidence and the policy: what do we know about cannabis use and what should we do?
Version of Record online: 9 FEB 2010
© 2010 The Authors. Journal compilation © 2010 Society for the Study of Addiction
Volume 105, Issue 8, pages 1326–1330, August 2010
How to Cite
Macleod, J. and Hickman, M. (2010), How ideology shapes the evidence and the policy: what do we know about cannabis use and what should we do?. Addiction, 105: 1326–1330. doi: 10.1111/j.1360-0443.2009.02846.x
- Issue online: 9 JUL 2010
- Version of Record online: 9 FEB 2010
- Submitted 16 July 2009; initial review completed 2 September 2009; final version accepted 19 October 2009
- public health;
In the United Kingdom, as in many places, cannabis use is considered substantially within a criminal justice rather than a public health paradigm with prevention policy embodied in the Misuse of Drugs Act. In 2002 the maximum custodial sentence tariff for cannabis possession under the Act was reduced from 5 to 2 years. Vigorous and vociferous public debate followed this decision, centred principally on the question of whether cannabis use caused schizophrenia. It was suggested that new and compelling evidence supporting this hypothesis had emerged since the re-classification decision was made, meaning that the decision should be reconsidered. The re-classification decision was reversed in 2008. We consider whether the strength of evidence on the psychological harms of cannabis has changed substantially and discuss the factors that may have influenced recent public discourse and policy decisions. We also consider evidence for other harms of cannabis use and public health implications of preventing cannabis use. We conclude that the strongest evidence of a possible causal relation between cannabis use and schizophrenia emerged more than 20 years ago and that the strength of more recent evidence may have been overstated—for a number of possible reasons. We also conclude that cannabis use is almost certainly harmful, mainly because of its intimate relation to tobacco use. The most rational policy on cannabis from a public health perspective would seem to be one able to achieve the benefit of reduced use in the population while minimizing social and other costs of the policy itself. Prohibition, whatever the sentence tariff associated with it, seems unlikely to fulfil these criteria.