Canada's Post-Legalization Adverse Reaction Reports Reveal Patterns in Cannabis Side Effects

What the researchers found

Among 698 adverse reaction reports to the Canada Vigilance Program, the average reporting individual was 56 years old, 45.4% were female, and 67.5% reported medical use (mainly pain management). Most cases (62.3%) were reported as serious, and 68.8% involved cannabis extracts. THC-dominant products were associated with different side effect profiles than CBD-dominant products. Common adverse events included hallucination, headache, nausea, dizziness, and dyspnea.

Why it matters

Canada's legalization framework included pharmaceutical-grade post-market surveillance for cannabis, making this the first large-scale adverse reaction reporting dataset from a legal regulated market. The data reveal that most reports come from older medical users of cannabis extracts, not recreational users, and that product composition matters for side effect profiles.

The numbers in context

698 unique adverse reaction reports. Mean age 56 years. 45.4% female. 67.5% medical use. 62.3% classified as serious. 68.8% involved extracts. Pain management was the top medical reason. Most events assessed as "possibly" related to cannabis.

How the study worked

Descriptive analysis of spontaneous adverse reaction reports submitted to Canada's post-market surveillance system since cannabis legalization in October 2018. Each case was assessed for causality. Data were aggregated to identify demographic patterns, product types involved, and event frequencies. Reports were from the Canada Vigilance Program's standardized pharmacovigilance framework.

What this study cannot tell us

Spontaneous reporting captures a small fraction of actual adverse events. Reports are subject to reporting bias. "Serious" classification includes "other medically important condition," which may not always reflect clinical severity. Cannot determine adverse event rates or compare to overall user population.

How to read the evidence

Moderate: large pharmacovigilance dataset from a regulated national system, though spontaneous reporting inherently underestimates actual adverse events.

When this study was published

2025 study (data from 2018 onward)

The bigger picture

Spontaneous reporting systems capture only a fraction of actual adverse events, but they can identify emerging safety signals. The predominance of older medical users in these reports may reflect both this population's higher engagement with healthcare and greater vulnerability to side effects, rather than indicating recreational products are safer.

Questions still open

• Why do cannabis extracts dominate adverse reports compared to dried flower? Are older medical users more vulnerable to side effects, or just more likely to report? How do Canadian adverse event patterns compare to other legal markets?

Common questions

Read the original research

Trends in cannabis adverse reaction reports: A descriptive analysis of spontaneous reporting data submitted to the Canada Vigilance Program since legalization and regulation of cannabis for non-medical purposes in Canada.

Journal of cannabis research, 7(1), 56

Citation

Plebon-Huff, Sieara; Aziz, Nadia; Cavar, Marko; Hassan, Safia; Aoun, Maria; Perwaiz, Shahid; Abramovici, Hanan. (2025). Trends in cannabis adverse reaction reports: A descriptive analysis of spontaneous reporting data submitted to the Canada Vigilance Program since legalization and regulation of cannabis for non-medical purposes in Canada.. Journal of cannabis research, 7(1), 56. https://doi.org/10.1186/s42238-025-00310-x

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