Cannabis Legalization and Opioid Use Disorder in Veterans Health Administration Patients

Abstract

Importance: In the context of the US opioid crisis, factors associated with the prevalence of opioid use disorder (OUD) must be identified to aid prevention and treatment. State medical cannabis laws (MCL) and recreational cannabis laws (RCL) are potential factors associated with OUD prevalence.

Objective: To examine changes in OUD prevalence associated with MCL and RCL enactment among veterans treated at the Veterans Health Administration (VHA) and whether associations differed by age or chronic pain.

Design, setting, and participants: Using VHA electronic health records from January 2005 to December 2022, adjusted yearly prevalences of OUD were calculated, controlling for sociodemographic characteristics, receipt of prescription opioids, other substance use disorders, and time-varying state covariates. Staggered-adoption difference-in-difference analyses were used for estimates and 95% CIs for the relationship between MCL and RCL enactment and OUD prevalence. The study included VHA patients aged 18 to 75 years. The data were analyzed in December 2023.

Main outcome and measures: International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) or International Statistical Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) OUD diagnoses.

Results: From 2005 to 2022, most patients were male (86.7.%-95.0%) and non-Hispanic White (70.3%-78.7%); the yearly mean age was 61.9 to 63.6 years (approximately 3.2 to 4.5 million patients per year). During the study period, OUD decreased from 1.12% to 1.06% in states without cannabis laws, increased from 1.13% to 1.19% in states that enacted MCL, and remained stable in states that also enacted RCL. OUD prevalence increased significantly by 0.06% (95% CI, 0.05%-0.06%) following MCL enactment and 0.07% (95% CI, 0.06%-0.08%) after RCL enactment. In patients aged 35 to 64 years and 65 to 75 years, MCL and RCL enactment was associated with increased OUD, with the greatest increase after RCL enactment among older adults (0.12%; 95% CI, 0.11%-0.13%). Patients with chronic pain had even larger increases in OUD following MCL (0.08%; 95% CI, 0.07%-0.09%) and RCL enactment (0.13%; 95% CI, 0.12%-0.15%). Consistent with overall findings, the largest increases in OUD occurred among patients with chronic pain aged 35 to 64 years following the enactment of MCL and RCL (0.09%; 95% CI, 0.07%-0.11%) and adults aged 65 to 75 years following RCL enactment (0.23%; 95% CI, 0.21%-0.25%).

Conclusions and relevance: The results of this cohort study suggest that MCL and RCL enactment was associated with greater OUD prevalence in VHA patients over time, with the greatest increases among middle-aged and older patients and those with chronic pain. The findings did not support state cannabis legalization as a means of reducing the burden of OUD during the ongoing opioid epidemic.

Figure 1.. Trends in Prevalence of Opioid Use Disorder (OUD) Among Veterans Health Administration Patients From 2005 to 2022 by Medical Cannabis Law (MCL)/Recreational Cannabis Law (RCL) Status

Overall trend in OUD as a function of cannabis law status from 2005 to 2022. In 2015, the predicted diagnostic prevalence of OUD is an aggregate across some patients with a diagnosis coded with International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) and others with International Statistical Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) due to the change in ICD coding midyear. Estimates were adjusted for age, sex, race and ethnicity, mandatory prescription drug monitoring program access law, receipt of 30 days or longer of prescription opioids, other substance use disorder (alcohol use disorder, cocaine use disorder, stimulant use disorder, sedative use disorder, hallucinogen related disorders, inhalant-related disorders, or other psychoactive substance–related disorder), and time-varying state covariates, including yearly state-level median income and yearly state rates of male individuals, Black individuals, Hispanic individuals, White individuals, those in the poverty category, those 18 years and older, and those who are unemployed. Error bars indicate 95% CIs. CL indicates cannabis law.

Figure 2.. State-Specific Associations of Medical Cannabis Law (MCL) and Recreational Cannabis Law (RCL) Enactment With Opioid Use Disorder in Veterans Health Administration Patients by the Most Recent Month per Year of Cannabis MCL or RCL Enactment

Estimates adjusted for age, sex, race and ethnicity, mandatory prescription drug monitoring program access law, receipt of 30 days or longer of prescription opioids, other substance use disorder (alcohol use disorder, cocaine use disorder, stimulant use disorder, sedative use disorder, hallucinogen related disorders, inhalant-related disorders, or other psychoactive substance–related disorder), and time-varying state covariates, including yearly state-level median income and yearly state rates of male individuals, Black individuals, Hispanic individuals, White individuals, those in the poverty category, those 18 years and older, and those who are unemployed. In states that changed to MCL and RCL during the period, the MCL/RCL association plotted was compared with no cannabis law (CL) for comparison with the MCL only vs no CL association. Point estimates and 95% CIs from the staggered-adoption difference-in-difference (DiD) regression models are displayed. From 2005 to 2022, 26 states and Washington, DC, enacted MCL only from 2005 to 2022 and 11 states and Washington, DC, transitioned from MCL only to RCL/MCL. Three states and Washington, DC, made both changes between 2005 and 2022 (ie, no CL to MCL only and then later to RCL/MCL) and therefore contributed data to both associations. There were 15 states (2 with MCLs only and 13 with no CLs in 2022) that made no law changes between 2005 and 2022; in the DiD model, they contributed to background secular trends. Model estimated effects represent the absolute increase or decrease in OUD prevalence associated with law enactment. The DiD model compared the years after enactment (up to 2022 or until the next law change) in each state to the years before enactment (since 2005 or the previous law change) in the same state and controls for contemporaneous trends in other states that have not yet passed the respective law.