Cannabis Legalisation Linked to More Use Among Adults and More Emergency Harms, but Adolescent Use Appears Largely Unchanged

A 2025 narrative review in The Lancet Public Health synthesises evidence from North America on the public health effects of adult cannabis legalisation, finding acute poisoning and emergency department visits rising sharply, adult use increasing modestly, and youth use trends remaining mixed and inconclusive across jurisdictions.

Why This Matters

Cannabis legalisation is accelerating globally, with over two dozen US states and Canada now permitting adult recreational use, yet the public health consequences remain incompletely characterised. Clinicians, especially those managing paediatric emergencies and substance use disorders, need reliable evidence about which harms are actually increasing and which fears may be overstated. This review arrives at a moment when regulatory frameworks are still being refined and when the gap between political momentum and clinical evidence is widening, making careful synthesis of the available data unusually consequential.

Clinical Summary

Adult cannabis legalisation in North America has unfolded as a natural policy experiment, with Canada legalising nationally in 2018 and individual US states beginning as early as 2014. This narrative review, published in The Lancet Public Health in 2025, draws on 12 selected systematic reviews rated moderate to high quality and supplementary primary studies to examine outcomes across multiple domains including cannabis use prevalence, cannabis use disorder, acute poisoning, emergency department visits, maternal use, and arrests. The mechanistic logic underlying the review is straightforward: commercialisation increases product availability, reduces price, and normalises use, which in turn should increase consumption and downstream harms, particularly from novel high-potency and edible products that are attractive to naive users and children.

The most consistent finding is a sharp rise in acute cannabis poisonings following legalisation, with an overall relative risk of approximately 3.56 and a paediatric relative risk of 4.31. In Ontario specifically, paediatric emergency department poisoning visits increased more than ninefold after commercial edible sales began compared with the pre-legalisation period. Adult cannabis use increased modestly, with Canadian past-three-month use rising from 14% in 2018 to 20% in 2020, while adolescent use showed no consistent change across most studies. Evidence on cannabis use disorder was mixed, and cannabis-related arrests declined substantially. The authors acknowledge that short follow-up periods, predominantly observational designs, and heterogeneous regulatory models across jurisdictions prevent causal attribution. They call for longer-term, standardised monitoring before firm policy conclusions can be drawn.

Dr. Caplan’s Take

This review gets right the thing that matters most clinically: the paediatric poisoning data is striking and biologically plausible. Edible products that look like candy and contain substantial THC doses are a foreseeable hazard, and the ninefold increase in Ontario paediatric ED visits after edible sales began is not an artefact of coding changes. When patients or parents ask me whether legalisation has made cannabis safer, I have to be honest that the regulatory environment has created specific new risks, particularly for young children in households where edibles are accessible. At the same time, this is a narrative review with explicitly stated directional assumptions, not a systematic review with pre-registered methods, so I weigh its broader claims about adult use trends and disorder prevalence with appropriate caution.

In practice, I counsel every patient with children at home about safe storage of cannabis products with the same urgency I bring to firearm and medication safety discussions. For adult patients considering cannabis, I focus on the distinction between lower-risk use patterns and the concentrated or edible products that dominate commercial markets. The evidence does not yet support sweeping clinical prohibitions based on legalisation per se, but it absolutely supports targeted harm reduction around product form, potency, and household access.

Clinical Perspective

This review sits at the synthesis stage of a still-maturing research arc. Most underlying studies are ecological or cross-sectional, with follow-up periods too short to capture chronic outcomes such as long-term cannabis use disorder progression, psychosis incidence, or cardiovascular effects. What the evidence supports with reasonable confidence is that acute poisonings, particularly paediatric ones tied to edible products, represent a real and growing clinical burden. What it does not support is any firm conclusion about whether legalisation increases cannabis use disorder at the population level, whether adolescent use trajectories are meaningfully altered, or whether longer-term health outcomes will worsen. Clinicians should avoid presenting the poisoning data and the use-prevalence data as carrying equivalent evidentiary weight.

From a pharmacological standpoint, the rise in poisoning severity is consistent with the high THC concentrations in commercial edibles, which can deliver 10 to 100 mg per serving compared with the 2 to 5 mg that produces effects in THC-naive individuals. Paediatric patients are especially vulnerable given lower body weight and immature hepatic metabolism. There are no specific drug interaction concerns unique to the legalisation context, but clinicians should be aware that patients may underreport edible use, particularly pregnant and breastfeeding women, given shifting social norms. One concrete, actionable step: integrate cannabis product storage counselling into well-child and prenatal visits, treating edibles with the same anticipatory guidance framework used for household toxins and medications.

Study at a Glance

Study Type

Narrative review with policy argument

Population

Adults, adolescents, and children in Canada and 24 US states with legalised adult cannabis use

Intervention

Adult-use (recreational) cannabis legalisation and commercial sales

Comparator

Pre-legalisation periods and non-legalised jurisdictions

Primary Outcomes

Cannabis use prevalence, cannabis use disorder, acute poisoning, ED visits, maternal use, arrests

Sample Size

12 selected systematic reviews plus supplementary primary studies

Journal

The Lancet Public Health

Year

2025

DOI or PMID

Not provided in source material

Funding Source

Not reported

What Kind of Evidence Is This

This is a policy-oriented narrative review, not a systematic review. It follows the NASEM evidence-review framework but does not conduct its own systematic literature search, apply pre-specified inclusion or exclusion criteria, or pool data meta-analytically. Narrative reviews occupy a lower tier in the evidence hierarchy than systematic reviews or meta-analyses because the selection and weighting of included studies are not fully transparent. The single most important inference constraint this imposes is that the directionality of findings may reflect the authors’ explicitly stated assumptions about commercialisation and harm rather than a comprehensive and unbiased reading of all available evidence.

How This Fits With the Broader Literature

The paediatric poisoning findings are consistent with prior work by Myran and colleagues documenting sharp increases in cannabis-related emergency visits in Canadian children following edible product availability, and with US poison control centre data showing similar post-legalisation trends. The adolescent use findings align with the 2019 NASEM report and a 2022 systematic review by Melchior and colleagues, both of which found limited evidence that legalisation increases teen cannabis consumption. Where this review extends the literature is in its attempt to integrate Canadian and US evidence across multiple outcome domains simultaneously, though this breadth comes at the cost of the depth and methodological rigour that domain-specific systematic reviews provide.

Common Misreadings

The most likely overinterpretation is to conclude that cannabis legalisation has been demonstrated to cause widespread public health harm across all populations. While the acute poisoning data, particularly for children, is compelling and consistent, the evidence on adult cannabis use disorder is mixed, adolescent trends are largely unchanged, and longer-term outcomes have not been studied. Equally, it would be a misreading to treat the review’s findings as equivalent to those of a systematic review or meta-analysis. The authors’ stated assumption that commercialisation inherently increases use and harm shapes the framing, and this should be understood as a directional argument supported by observational evidence rather than as a settled causal conclusion.

Bottom Line

This review provides a useful if methodologically limited snapshot of early post-legalisation evidence from North America. Its strongest contribution is documenting the sharp rise in paediatric cannabis poisonings, particularly after edible products entered commercial markets. It does not establish that legalisation causes population-level increases in cannabis use disorder or adolescent uptake. For clinicians, the actionable signal is clear: anticipatory guidance around safe storage of cannabis edibles should be standard practice, while broader claims about legalisation and health require longer follow-up and stronger study designs before they can inform clinical recommendations.

References

1. The Lancet Public Health narrative review on adult cannabis legalisation and public health effects in Canada and the USA (2025). The Lancet Public Health. Full citation details and DOI not provided in source material.
2. Myran DT, et al. Edible cannabis legalisation and paediatric emergency department visits. Various publications documenting Ontario and Canadian poison control data post-legalisation.
3. National Academies of Sciences, Engineering, and Medicine (NASEM). The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington, DC: The National Academies Press; 2017.
4. Melchior M, et al. Systematic review on cannabis legalisation and adolescent use (2022). Referenced in the narrative review as part of the evidence base for adolescent outcomes.