In a recent study posted to the medRxiv pre-print* server, a team of researchers analyzed trends in cannabis use among United States (U.S.) adults with/without severe psychological distress (SPD) (2009-2019) and its link to psychiatric hospitalizations and outpatient mental health care.
Study: Disproportionate increase in cannabis use among individuals with serious psychological distress and association with psychiatric hospitalization and outpatient service use in the National Survey on Drug Use and Health 2009-2019. Image Credit: solarseven / Shutterstock
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Background
The World Health Organization (WHO) reports that 147 million people, or 2.5% of the total population, use cannabis, and its growing popularity poses a risk, especially for those with mental health problems. Its use is associated with a higher risk of psychosis and negative symptoms in schizophrenia, as well as recently noted links to anxiety and mood disorders. SPD People with high incidences of cannabis and substance use disorders are at greater risk for serious mental illness, health deterioration, and more severe drug abuse. SPD individuals used slightly more cannabis between 2008 and 2016, but the subsequent impact on psychiatric services is still unclear. However, with legalization and attitudinal change, further research is needed on changing cannabis use patterns to clarify their effect on mental health.
About the study
Data for the present study was sourced from the National Survey on Drug Use and Health (NSDUH) public use files spanning 2009 to 2019. A comprehensive cross-sectional survey conducted in the United States collects detailed data on demographics, substance use, mental health disorders, and health service utilization. The NSDUH excludes a small number of specific populations from its sample, such as prison inmates or homeless persons who live outside the community where they grew up into adulthood. From the total of 619,411 respondents, the study focused on 444,947 adults aged 18 and above.
The primary metric evaluated was the frequency of cannabis use, divided into two categories: Any use over the last year. One-weekly or more frequent use only. The study also measured the use of outpatient and inpatient mental health services. The central variable for analysis was SPD in the past year, determined using the Kessler Serious Psychological Distress scale (K6). This scale identifies SPD based on scores, with a threshold distinguishing significant psychiatric disorders.
The study accounted for changes in substance use over time, incorporating survey years into its model. Other predictors in the analysis included demographic factors such as sex, income, race, age, marital status, education level, and heavy alcohol use. As for those with SPD, the amount of cannabis used was an important factor in analyzing psychiatric service use.
Statistical procedures included chi-squared tests, logistic regression models with interaction terms, and predictive margins method for understanding nonlinear model interactions. Weights were adjusted for non-response and consistency with U.S. Census Bureau data in the determination of sampling weights. p<0.05 was considered to indicate significance, and all analyses were performed using Stata (version 16).
Study results
In the detailed analysis of individuals with and without SPD, it was found that those with SPD exhibited higher rates of cannabis use. Specifically, 27.4% of individuals with SPD engaged in any cannabis use compared to 11.7% without SPD, and 13.9% used cannabis weekly or more, versus 5.6% among those without SPD. Notably, significant differences were observed between these groups across various demographic and socioeconomic characteristics.
Analyzing how cannabis use has changed over time, especially between 2009 and 2019, produced clear trends. A similar trend was shown by unadjusted rates up to and including 2014. However, since 2015, the rate of increase in cannabis use among people with SPD increased markedly. In particular, there was an increase of 5.0 % higher than the control group in 2019 for those who already had SPD; that is to say that cannabis use had accelerated even faster among these latter individuals over this more recent period.
Furthermore, it was even true when narrowing the focus to weekly or more cannabis use. The findings showed an equivalent rise in the two groups up to 2014, but those with SPD rose much more sharply from then onwards. This trend indicates that the habits of cannabis use are becoming farther and wider apart between those with SPD, who account for most smokers, versus non-SPD users.
The study also explored the relationship between using cannabis and taking advantage of psychiatric services for individuals with SPD. Controlling for various independent variables, there is a higher incidence of inpatient psychiatric hospitalization among cannabis users than non-users; less frequent and weekly-plus categories both have significantly heightened probabilities. In addition, there was no apparent difference in the risk of hospitalization between less frequent and more frequent cannabis users.
As for outpatient psychiatric care, less than weekly cannabis users and those with at least a weekly habit were both more likely to receive it compared to non-users. In addition, users who have fewer than weekly outpatient clinic visits have more hospital visits.
An exploratory analysis was conducted to understand if perceptions of risk associated with cannabis use could explain the observed differences in use among those with and without SPD. This analysis, which included perceptions of the risk of monthly and weekly cannabis use, showed that while risk perceptions partially influenced the relationship between SPD and cannabis use, they did not fully account for the differences observed in the changes in rates of use between the two groups. This finding suggests that other factors may also influence these trends.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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