Cannabis and Psychosis: Recent Epidemiological Findings Continuing the “Causality Debate”

Abstract

Nonmedical (“recreational”) cannabis use and cannabis laws have changed over the past two decades in the United States (1) and the rest of the world (2). Increasing use, especially among the young, coupled with the increasing potency of cannabis (higher delta-9-tetrahydrocannabinol [THC] content) during this period (3), has raised concerns about the long-term health impact of cannabis exposure, especially among adolescents and young adults. There is recognition of an association between cannabis use and psychosis, but whether the relationship is causal continues to be debated. One rebuttal raised in this debate is that if cannabis caused psychosis, then the increases in the rates of cannabis use should be accompanied by a parallel increase in the rates of psychosis.

The article by Livne et al. (4) in this issue of the Journal is the first report from a U.S. sample of an increase in the prevalence of self-reported psychotic disorders. The authors report an approximately 2.5-fold increase in the prevalence of self-reported psychosis when comparing nationally representative data from National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) conducted in 2001–2002 (NESARC) and in 2012–2013 (NESARC-III) (5). The question on self-reported psychosis, unlike those on self-reported symptoms of psychosis, asks respondents whether they have been diagnosed with schizophrenia or a related psychotic disorder by a doctor or other health professional. The authors addressed dose-response by examining the relationship between proxy measures of dose (cannabis use frequency: any use, frequent use, daily use; and cannabis use disorder) and self-reported psychosis in NESARC and NESARC-III and any change in the magnitude of the relationship between the two surveys. They noted that compared with nonusers, those with any use and with cannabis use disorder were at increased risk of self-reported psychosis during NESARC. In comparison to NESARC, survey respondents in all four use categories were at higher risk of self-reported psychosis during NESARC-III. Lastly, no statistically significant differences were noted in the magnitudes of the estimates of relationships between the two waves of the survey.