Cannabis Poisoning and Mental Health Crises Were Rare Among Medical Cannabis Patients in Ontario | Research

The takeaway

Among 23,091 medically authorized cannabis patients in Ontario, cannabis poisoning-related ER visits occurred at a rate of 8 per 10,000 person-years and cannabis-related mental health ER visits at 15 per 10,000 person-years, with prior substance use and mental health disorders being the strongest predictors.

Medical cannabis patients and clinicians assessing the safety of authorized cannabis use

23,091 patients, low event rates

What the researchers found

During a median follow-up of 240 days, only 14 patients visited the ER or were hospitalized for cannabis poisoning (8.06 per 10,000 person-years) and 26 for cannabis-related mental and behavioral disorders (15.0 per 10,000 person-years). Predictors of cannabis-related mental health events included prior substance use disorders, other mental disorders, age, diabetes, and COPD.

Why it matters

As medical cannabis programs expand, quantifying the rate of acute harms helps patients and clinicians weigh risks. The low overall rates of poisoning and mental health crises in this medically supervised population are reassuring, while the identified risk factors can guide monitoring.

The numbers in context

23,091 patients; median 240 days follow-up; 14 cannabis poisoning ER visits (8.06/10,000 person-years); 26 mental/behavioral disorder ER visits (15.0/10,000 person-years); prior substance use disorders strongest predictor

How the study worked

Retrospective cohort study of patients who received medical cannabis authorization in Ontario, Canada between 2014-2017. Data from participating cannabis clinics linked to health administrative data. Cox proportional hazard regressions used to identify predictors.

What this study cannot tell us

Retrospective design with clinic-collected data may miss patients who sought care elsewhere. Short median follow-up of 240 days may underestimate long-term risks. No control group for comparison. Only captures events severe enough to prompt ER visit or hospitalization.

How to read the evidence

Large retrospective cohort with clinical data, but no control group and short follow-up period

When this study was published

2022 study

The bigger picture

These findings suggest that medical cannabis, when used under clinical authorization, carries a low rate of acute serious harms. However, patients with pre-existing substance use or mental health disorders face higher risk and may need closer monitoring.

Questions still open

How do these rates compare to non-medical cannabis users? Would longer follow-up reveal increasing rates over time? Could pre-authorization screening for risk factors reduce acute events?

Common questions

How safe is medical cannabis for authorized patients?

In this study, acute harms requiring ER visits were rare: about 8 per 10,000 person-years for poisoning and 15 per 10,000 for mental health crises. However, patients with prior substance use or mental health disorders faced higher risk.

Who is most at risk for problems with medical cannabis?

The strongest predictors were prior substance use disorders and other mental health disorders. Age, diabetes, and COPD were also associated with higher risk of cannabis-related mental health events.

Read the original research

Incidence and Predictors of Cannabis-Related Poisoning and Mental and Behavioral Disorders among Patients with Medical Cannabis Authorization: A Cohort Study.

Substance use & misuse, 57(10), 1633-1641

View on PubMed ↗Publisher’s paper ↗

Citation

Zongo, Arsene; Lee, Cerina; Dyck, Jason R B; El-Mourad, Jihane; Hyshka, Elaine; Hanlon, John G; Eurich, Dean T. (2022). Incidence and Predictors of Cannabis-Related Poisoning and Mental and Behavioral Disorders among Patients with Medical Cannabis Authorization: A Cohort Study.. Substance use & misuse, 57(10), 1633-1641. https://doi.org/10.1080/10826084.2022.2102193