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CME / ABIM MOC / CE

Cannabis Use and Psychosis? It’s Not All Good News

  • Authors: News Author: Megan Brooks; CME Author: Laurie Barclay, MD
  • CME / ABIM MOC / CE Released: 5/3/2019
  • Valid for credit through: 5/3/2020
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  • Credits Available

    Physicians - maximum of 0.25 AMA PRA Category 1 Credit(s)™

    ABIM Diplomates - maximum of 0.25 ABIM MOC points

    Nurses - 0.25 ANCC Contact Hour(s) (0.25 contact hours are in the area of pharmacology)

    Pharmacists - 0.25 Knowledge-based ACPE (0.025 CEUs)

    You Are Eligible For

    • Letter of Completion
    • ABIM MOC points

Target Audience and Goal Statement

This article is intended for primary care physicians, psychiatrists, emergency medicine physicians, neurologists, nurses, pharmacists, public health and prevention officials, and other members of the healthcare team who care for cannabis users.

The goal of this activity is to provide medical news to primary care clinicians and other healthcare professionals in order to enhance patient care.

Upon completion of this activity, participants will be able to:

  • Describe patterns of cannabis use with the strongest effect on risks for psychotic disorder and the contribution of differences in such patterns to marked regional variations in the incidence rates of psychotic disorder, according to a case-control study at multiple sites across Europe
  • Determine clinical and public health implications of the association between cannabis use and incidence rates of psychotic disorder, according to a case-control study at multiple sites across Europe


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Medscape, LLC, encourages Authors to identify investigational products or off-label uses of products regulated by the US Food and Drug Administration, at first mention and where appropriate in the content.


News Author

  • Megan Brooks

    Freelance writer, Medscape LLC

    Disclosures

    Disclosure: Megan Brooks has disclosed no relevant financial relationships.

CME Author

  • Laurie Barclay, MD

    Freelance writer and reviewer, Medscape, LLC

    Disclosures

    Disclosure: Laurie Barclay, MD, has disclosed no relevant financial relationships.

Editor/CME Reviewer

  • Esther Nyarko, PharmD

    Associate CME Clinical Director, Medscape, LLC

    Disclosures

    Disclosure: Esther Nyarko, PharmD, has disclosed no relevant financial relationships.

Nurse Planner

  • Amy Bernard, MS, BSN, RN-BC, CHCP

    Lead Nurse Planner, Medscape, LLC

    Disclosures

    Disclosure: Amy Bernard, MS, BSN, RN-BC, CHCP, has disclosed no relevant financial relationships.


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    Successful completion of this CME activity, which includes participation in the evaluation component, enables the participant to earn up to 0.25 MOC points in the American Board of Internal Medicine's (ABIM) Maintenance of Certification (MOC) program. Participants will earn MOC points equivalent to the amount of CME credits claimed for the activity. It is the CME activity provider's responsibility to submit participant completion information to ACCME for the purpose of granting ABIM MOC credit.

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CME / ABIM MOC / CE

Cannabis Use and Psychosis? It’s Not All Good News

Authors: News Author: Megan Brooks; CME Author: Laurie Barclay, MDFaculty and Disclosures

CME / ABIM MOC / CE Released: 5/3/2019

Valid for credit through: 5/3/2020

processing....

Clinical Context

Recent legalization or decriminalization of cannabis use in many countries have resulted in concerns regarding the potential for increased use and associated harm. A causal link with dose-response association between cannabis use and psychotic disorder is supported by cross-sectional and prospective epidemiological studies, biological evidence, and meta-analysis.

Although cannabis use is associated with increased risk for subsequent psychotic disorder, it is still undetermined whether it affects incidence of the disorder. The goal of this case-control study across Europe was to identify patterns of cannabis use with the strongest effect on risks for psychotic disorder and to examine whether differences in such patterns contribute to marked regional variations in the incidence rates of psychotic disorder.

Study Synopsis and Perspective

Daily use of cannabis, particularly high potency cannabis, is associated with higher rates of psychosis, new research shows.

In the first study to show the effect of cannabis use at a population level, investigators found daily users of high-potency cannabis were up to 5 times more likely to have first-episode psychosis (FEP) than noncannabis users.

"Differences in frequency of daily cannabis use and in use of high potency cannabis contributed to the striking variation in the incidence of psychotic disorder across the 11 sites we studied across Europe," lead investigator Marta Di Forti, MD, PhD, of the Institute of Psychiatry, Psychology, and Neuroscience, at King's College London, UK, told Medscape Medical News.

In cities where high-potency cannabis is widely available, such as London and Amsterdam, a significant proportion of new cases of psychosis are associated with daily cannabis use and high-potency cannabis. High-potency cannabis use may be linked to half of all new cases of psychosis in Amsterdam and about a third in London, the findings suggested.

"This has important implications for public health, given the increasing availability of high potency cannabis," said Dr Di Forti.

The study was published online March 19 in Lancet Psychiatry.[1]

Mental Health Harms

The researchers examined detailed measures of cannabis use from 901 patients with FEP and 1237 healthy matched control participants.

Daily cannabis use was more common in people with FEP compared with control participants (29.5% vs 6.8%). High-potency cannabis use (Δ6-tetrahydrocannabinol [THC] ≥10%) was also more common among people with FEP compared with control participants (37.1% vs 19.4%).

Across the 11 sites, daily cannabis users were 3 times more likely to have FEP than never users (adjusted odds ratio [aOR]=3.2 [95% CI: 2.2, 4.1]). Daily users of high-potency cannabis were nearly 5 times more likely to have FEP than never users (aOR=4.8 [95% CI: 2.5, 6.3]).

"Our findings are consistent with previous studies showing that the use of cannabis with a high concentration of THC has more harmful effects on mental health than the use of weaker forms," said Dr Di Forti.

In addition, the authors calculated the "population attributable fraction [(PAF)]," which estimates the contribution of cannabis use to psychosis rates in a population and the proportion of cases that would be prevented if the exposure were removed.

Across all 11 cities, they estimate that 1 in 5 (20.4%) new cases of psychosis may be linked to daily cannabis use and approximately 1 in 10 (12.2%) to use of high-potency cannabis.

In Amsterdam, 1 in 4 (43.8%) new cases of psychosis may result from daily cannabis use and 5 in 10 (50.3%) from high-potency cannabis use. Corresponding rates in London were 21% for daily use and 30.3% for high-potency use.

Assuming causality, if high-potency cannabis were no longer available, the incidence of psychosis would drop significantly from 37.9 to 18.8 per 100,000 people per year in Amsterdam and from 45.7 to 31.9 per 100,000 people per year in London, the researchers calculated.

Cautionary Notes

Commenting on the findings for Medscape Medical News, Suzanne Gage, PhD, University of Liverpool, England, United Kingdom, offered 2 "key cautionary notes" on the study.

"Firstly, THC levels in cannabis were not measured directly but rather ascertained through a combination of self-report and what is known about the levels of seized cannabis in the areas in question from other sources. And secondly, the comparisons of cannabis use and prevalence of psychosis in the different regions are based on very small samples of cannabis users," she told Medscape Medical News.

In an accompanying editorial,[2] Dr Gage questioned whether the study provides certainty that daily and high-potency cannabis use causes psychosis.

"Unfortunately, not all the evidence utilizing different methods is consistent about causality. It is perfectly possible that the association between cannabis and psychosis is bidirectional," she wrote.

"Di Forti and colleagues' study adds a new and novel study design to the evidence available, which consistently indicates that for some individuals there is an increased risk of psychosis resulting from daily use of high potency cannabis. Given the changing legal status of cannabis across the world, and the associated potential for an increase in use, the next priority is to identify which individuals are at risk from daily potent cannabis use, and to develop educational strategies and interventions to mitigate this," Gage concluded.

The study was funded by the Medical Research Council, the European Community’s Seventh Framework Program grant, Sao Paolo Research Foundation, National Institute for Health Research (NIHR) Biomedical Research Centre (BRC) at South London and Maudsley NHS Foundation Trust and King’s College London, and the NIHR BRC at University College London, and the Wellcome Trust. Di Forti has reported receiving personal fees from Janssen-Cilag unrelated to the study. Gage has reported no relevant financial relationships.

Study Highlights

  • Cases were 901 patients between 18 and 64 years old presenting with FEP to psychiatric services at 11 sites across Europe and Brazil between May 1, 2010, and April 1, 2015.
  • Control participants (n=1237) representative of the local populations were matched by site and recruited.
  • To avoid selection and recall bias, none of the sites mentioned cannabis or other drug use in the materials used for participant recruitment.
  • Use of adjusted logistic regression models allowed estimation of which patterns of cannabis use were associated with the highest odds for psychotic disorder.
  • Cannabis use by participants was characterized as low-potency (Δ9-THC; THC <10%) and high-potency (THC ≥10%), according to European and national data on the expected THC concentration in different types of cannabis available across the sites.
  • PAFs were calculated assuming causality for the patterns of cannabis use associated with the highest odds for psychosis and the correlation between such patterns and the incidence rates for psychotic disorder across the study sites.
  • Compared with control participants, cases were more likely to use cannabis daily (29.5% vs 6.8%) and to use high-potency cannabis (37.1% vs 19.4%).
  • Compared with never users of cannabis, daily cannabis use was associated with increased odds for psychotic disorder (aOR=3.2 [95% CI: 2.2, 4.1]),.
  • The odds for psychotic disorder among users of high-potency cannabis were 1.6 times higher than for never users.
  • For daily use of high-potency types of cannabis, odds increased nearly 5-fold (aOR=4.8 [95% CI: 2.5, 6.3]).
  • Beginning cannabis use by age 15 years was associated with modestly increased odds for psychotic disorder, but this was not independent of frequency of use or of cannabis potency.
  • There was no apparent interaction of these measures of extent of exposure with each other or with the sites.
  • Among the measures of cannabis use tested, daily use and high-potency use were the strongest independent predictors of whether any given individual would or would not have a psychotic disorder.
  • Use of high-potency cannabis was a strong predictor of psychotic disorder in sites where this is widely available, such as Amsterdam, The Netherlands; London, England, United Kingdom; and Paris, France, but not in sites such as Palermo, Italy, where this type was not yet available.
  • If high-potency cannabis were no longer available, the proportion of cases of FEP that could be prevented was 12.2% across the 11 sites (95% CI: 3, 16.1), increasing to 30.3% in London (95% CI: 15.2, 40) and 50.3% in Amsterdam (95% CI: 27.4, 66), according to calculated PAFs.
  • Assuming causality, if high-potency cannabis were no longer available, the adjusted incidence rates for all psychotic disorder would decrease from 37.9 to 18.8 cases per 100 000 person-years in Amsterdam and from 45.7 to 31.9 cases per 100 000 person-years in London.
  • If daily use of cannabis were abolished, 20% of new cases of psychotic disorder across all sites could have been prevented, with PAF for daily use of 6% in Palermo, 21% for London, and 44% in Amsterdam.
  • Across the 11 sites, the adjusted incident rates for psychotic disorder were positively correlated with the prevalence in control participants s of use of high-potency cannabis (r =0.7; P =.0286) and daily use (r =0.8; P =.0109).
  • According to their findings, the investigators concluded that differences in frequency of daily cannabis use and in use of high-potency cannabis contributed to the marked variation in psychotic disorder incidence across the 11 studied sites.
  • The findings have important implications for public health, given the increasing availability of high-potency cannabis, and they confirm previous evidence of the harm to mental health of daily cannabis use, particularly of high-potency cannabis.
  • For the first time, this study shows how cannabis use can affect psychotic disorder incidence across multiple sites throughout Europe: in areas where daily use and use of high-potency cannabis are more common in the general population, there is an excess of cases of psychotic disorder.
  • Weighing the potential medicinal properties of some cannabis constituents against the potential adverse effects (AEs) of daily cannabis use, especially of high-potency types, is therefore of great public health importance.
  • Study limitations include possibly insufficient power to detect an interaction between degree of cannabis use and site; lack of biological validation of data on cannabis use; and lack of inclusion of cannabidiol in the potency variable.
  • An accompanying editorial noted additional limitations of lack of direct measurement of THC levels in cannabis; comparisons of cannabis use and prevalence of psychosis at different sites according to very small samples of cannabis users; and the possibility that the association between cannabis and psychosis is bidirectional rather than causal.
  • The editorial recommended that future research address how to identify persons at risk from daily potent cannabis use and development of educational strategies and interventions to reduce risk.

Clinical Implications

  • Differences in frequency of daily cannabis use and potency cannabis contributed to the marked variation in psychotic disorder incidence across 11 European sites used for a case-control study.
  • The findings have important implications for public health, given the increasing availability of high-potency cannabis, and they confirm previous evidence of the harm to mental health of daily cannabis use, particularly of high-potency cannabis.
  • Implications for the Healthcare Team: Weighing the potential medicinal properties of some cannabis constituents against the potential AEs of daily cannabis use, especially of high-potency types, is therefore of great public health importance.

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