Medical Cannabis Patients Had Higher Rates of ER Visits for Drug Poisoning Than Matched Controls
Medical cannabis patients in Ontario had 2.45 times the risk of ER visits for psychoactive drug poisoning and 2.27 times the risk for substance-related mental health disorders compared to matched population controls.
Quick Facts
What This Study Found
Among 18,653 medical cannabis patients matched to 51,243 controls, poisoning incidence was 4.71 per 1,000 person-years for cannabis patients vs 1.73 for controls (adjusted HR: 2.45, 95% CI: 1.56-3.84). Mental/behavioral disorder incidence was 8.89 vs 5.01 per 1,000 person-years (adjusted HR: 2.27, 95% CI: 1.66-3.11). No sex differences were observed.
Key Numbers
18,653 cannabis patients matched to 51,243 controls; poisoning: 4.71 vs 1.73 per 1,000 person-years (aHR 2.45); mental/behavioral disorders: 8.89 vs 5.01 per 1,000 (aHR 2.27); median 243 days follow-up; no sex differences
How They Did This
Retrospective cohort study matching 18,653 adult medical cannabis patients from Ontario clinics to 51,243 population-based controls. Outcomes were ER visits or hospitalizations for psychoactive drug poisoning and substance-related mental/behavioral disorders. Conditional Cox proportional hazards regressions used with median follow-up of 243 days.
Why This Research Matters
While the companion study (RTHC-04336) found low absolute rates of cannabis-specific harms, this study reveals that medical cannabis patients face elevated risk for broader substance-related problems compared to the general population, raising questions about pre-existing vulnerability versus cannabis-related risk.
The Bigger Picture
This elevated risk could reflect that medical cannabis patients have underlying conditions (chronic pain, mental health disorders) that independently increase substance-related risks, rather than cannabis itself causing the excess events. Disentangling these factors is crucial for medical cannabis policy.
What This Study Doesn't Tell Us
Cannot establish causation. Medical cannabis patients differ from the general population in ways beyond cannabis use (chronic pain, mental health conditions) that could explain higher ER visit rates. Short follow-up period. Matching may not fully control for confounding by indication.
Questions This Raises
- ?Does the elevated risk reflect pre-existing vulnerability in people who seek medical cannabis, or does cannabis itself increase risk?
- ?Would more comprehensive matching on comorbidities reduce the observed difference?
- ?How do these rates compare to patients on long-term opioid therapy?
Trust & Context
- Key Stat:
- 2.45x higher poisoning risk
- Evidence Grade:
- Large matched cohort study with administrative data, but confounding by indication remains a concern
- Study Age:
- 2022 study
- Original Title:
- Substance Use Disorders and Psychoactive Drug Poisoning in Medically Authorized Cannabis Patients: Longitudinal Cohort Study.
- Published In:
- Canadian journal of psychiatry. Revue canadienne de psychiatrie, 67(7), 544-552 (2022)
- Authors:
- Zongo, Arsène(3), Lee, Cerina(7), El-Mourad, Jihane(4), Dyck, Jason R B, Hyshka, Elaine, Hanlon, John G, Eurich, Dean T
- Database ID:
- RTHC-04337
Evidence Hierarchy
Looks back at existing records to find patterns.
What do these levels mean? →Frequently Asked Questions
Does medical cannabis increase the risk of drug poisoning?
Medical cannabis patients had 2.45 times the risk compared to matched controls, but this does not prove cannabis caused the excess risk. Patients who seek medical cannabis often have conditions that independently increase substance-related risks.
Were men or women more affected?
No sex differences were observed. Both men and women with medical cannabis authorization showed similarly elevated risks compared to their respective controls.
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Cite This Study
https://rethinkthc.com/research/RTHC-04337APA
Zongo, Arsène; Lee, Cerina; El-Mourad, Jihane; Dyck, Jason R B; Hyshka, Elaine; Hanlon, John G; Eurich, Dean T. (2022). Substance Use Disorders and Psychoactive Drug Poisoning in Medically Authorized Cannabis Patients: Longitudinal Cohort Study.. Canadian journal of psychiatry. Revue canadienne de psychiatrie, 67(7), 544-552. https://doi.org/10.1177/07067437211060597
MLA
Zongo, Arsène, et al. "Substance Use Disorders and Psychoactive Drug Poisoning in Medically Authorized Cannabis Patients: Longitudinal Cohort Study.." Canadian journal of psychiatry. Revue canadienne de psychiatrie, 2022. https://doi.org/10.1177/07067437211060597
RethinkTHC
RethinkTHC Research Database. "Substance Use Disorders and Psychoactive Drug Poisoning in M..." RTHC-04337. Retrieved from https://rethinkthc.com/research/zongo-2022-substance-use-disorders-and
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.