Has the Legalisation of Medical and Recreational Cannabis Use in the USA Affected the Prevalence of Cannabis Use and Cannabis Use Disorders?

Since California legalised medical use of cannabis in 1996, 29 other US states have done so. Eight US states have legalised the retail sale of cannabis to adults over the age of 21 years since 2012. Critics of these policy changes have suggested that they will increase the prevalence of cannabis use and cannabis use disorders. This paper (1) briefly describes the types of regulatory regimes for medical and recreational cannabis use in the USA, (2) describes possible effects of these policies on cannabis use and (3) assesses the impacts to date of the legalisation of medical and recreational cannabis use on the prevalence of cannabis use and cannabis use disorders in the US population. We (1) describe the regulatory regimes for medical and recreational cannabis use in the USA, (2) make predictions about their possible effects on the price and availability of cannabis, (3) conduct a review to summarise studies of the effects of legalising medical cannabis use in the USA on rates of cannabis use and cannabis use disorders and (4) assess early indications of the effects of legalising recreational cannabis use on cannabis use and cannabis use disorders.

Liberal forms of medical cannabis regulation have probably reduced prices and increased the availability of cannabis. Analyses of survey data suggest that these changes have increased the prevalence and frequency of cannabis use among adults over the age of 21 years, but they have not to date increased rates of cannabis use among adolescents. Two series of epidemiological studies over a decade following the introduction of medical cannabis laws have produced inconsistent results on the effects of policy changes on the prevalence of cannabis use disorders in adults. One study found that the prevalence had increased; the other did not find an increase. An analysis of data on treatment seeking for cannabis use disorders showed an increase in states with medical cannabis laws in the number of adults seeking treatment who were not under legal coercion. There are major limitations with these studies, many of which have mistakenly assumed that all states with medical cannabis laws have similarly liberal policies.

It may be a decade or more before we can fully assess the effects of liberalisation of cannabis policies on cannabis use and cannabis use disorders in the USA. It is critical that the effects of these policy changes are evaluated to ensure that cannabis is regulated in ways that minimise the harmful effects of its regular use, especially among young people.