Does Cannabis Psychosis Really Exist As Reclassification Affects Trends?

Cannabis has been initially assigned by the United Kingdom Misuse of Drugs Act in 1971 to Group B, where all controlled drugs were divided into other categories A and C, including criminal sanctions for every group. However, it was shifted to the lowest risk category Group C in 2004, and then later returned to Group B in 2009, citing the growing concerns regarding the relation between schizophrenia and the powerful cannabis.

The cannabis was subject to a study, which is aimed at testing the hypothesis that the changes made in the classification result in levels of psychosis. It specifically examines if both changes in 2009 and 2004 were related to changes in the amount of people diagnosed with cannabis psychosis, NPR reported.

The connection between the changes in the cannabis classification, including the effect in the admissions for cannabis psychosis in hospital were studied using the interrupted time series. Indicating both policy changes, the two interruptions were made to the time series.  The admission data in Hospital Episode Statistics were evaluated, which covered the period from 1999 to 2010.

A significant increase in the trend in hospital admissions for cannabis psychosis were revealed from 1999 to 2004. Yet, after cannabis was reclassified from B to C category in 2004, there was a notable change in the trend, as hospital admissions for cannabis psychosis were reduced in 2009. After the second reclassification of cannabis in 2009, turning it back to category B, a significant change was noted in the growth of admissions.

Cannabis' reclassification and the hospital admissions for cannabis psychosis were found to have a statistical relationship in contrasting direction to that expected by the assumed link between those two. Although the reasons for the statistical relations have not been identified yet, it is unlikely because of the changes of the cannabis usage over such period. Some possible reasons may be due to the changes in policy and systemic mental health services that are not related to classification matters,  according to IJDP.