"In my view, the association is most likely causative, at least to a large extent," Dr. Carsten Hjorthoj of the Mental Health Research Center Copenhagen in Hellerup told Reuters Health by email. "It is of course nearly impossible to use epidemiological studies to actually prove causation, but all the numbers behave exactly in the way that would be expected under the theory of causation."
"For instance," he said, "we show in the present study how the proportion of schizophrenia attributable to cannabis use has increased over time - which is fully what would be expected, seeing as how both the potency of cannabis and the proportion of cannabis users have increased."
As reported in JAMA Psychiatry, the registry-based study included all people in Denmark born before 2000 who were alive and 16 years or older at some point from 1972 through 2016. The primary aim was to determine whether the population-attributable risk fraction (PARF) of cannabis use disorder in schizophrenia has increased over time.
More than 7 million individuals were included in the analysis, split evenly between the sexes.
The adjusted hazard ratio for schizophrenia "fluctuated over time, but with no clear trend, and generally centered around an adjusted hazard ratio of approximately 4" when comparing those diagnosed with cannabis use disorder to those without, the researchers said. The association remained statistically significant throughout the study period.
The PARF of cannabis use disorder in schizophrenia also fluctuated; however, there was "clear evidence" of an increase from 1995, when the PARF was relatively stable at around 2%, until reaching some stability around 6% to 8% since 2010.
The PARF is an estimate of the proportion of schizophrenia cases that would have been prevented if no one had been exposed to cannabis use disorder, under the assumption that the association between the two might be causal, the authors explain. Given this assumption, as Dr. Hjorthoj indicated, the PARF cannot confirm whether an association is truly causal. However, an increase in the PARF co-occurring alongside an increase in either the proportion using cannabis or in the potency of cannabis would be expected if the association were causal.
The authors state, "The results from these longitudinal analyses show the proportion of cases of schizophrenia associated with cannabis use disorder has increased 3- to 4-fold during the past 2 decades, which is expected given previously described increases in the use and potency of cannabis. This finding has important ramifications regarding legalization and control of use of cannabis."
Dr. Hjorthoj said, "A particular focus of ours currently is to gain a deeper understanding of the concept of cannabis-induced psychosis. This disorder is directly triggered by cannabis use, and while different from schizophrenia per se, we expect a better understanding of both the epidemiology and neurobiology of this disorder to also have profound implications for the understanding of the cannabis-to-schizophrenia association."
Dr. Tyler VanderWeele of The Harvard T. H. Chan School of Public Health in Boston, author of a related editorial, commented by email to Reuters Health, "While the estimates indicate that the majority of schizophrenia cases are due to causes other than cannabis-use disorder, nevertheless probably at least 8%-10%, and possibly 30% or more, of schizophrenia cases in the study are due to cannabis use and this proportion has been increasing over time."
"Cannabis-use disorder is responsible for a non-negligible, and increasing, proportion of schizophrenia and this should be considered in discussions regarding legalization and regulation of the use of cannabis," Dr. VanderWeele concluded.
SOURCE: https://bit.ly/3x9Z9Ah and https://bit.ly/3xfpxcj JAMA Psychiatry, online July 21, 2021.
By Marilynn Larkin
Posted on
site created by:
© 2024 Medicom Medical Publishers. All rights reserved. Terms and Conditions | Privacy Policy