News Release

Cannabis poisonings rise after legalization, new review concludes

Peer-Reviewed Publication

Society for the Study of Addiction

A new meta-analysis (an analysis of past research) published by the scientific journal Addiction has found that cannabis legalisation is associated with increased rates of cannabis poisoning.  The risk of cannabis poisoning was higher among studies that focused on children.

Cannabis poisoning occurs when too much cannabis is consumed at one time.  The effects of cannabis poisoning include lethargy, drowsiness, dizziness, hypertension, palpitations, tachycardia (elevated heart rate), nausea, vomiting, irritability, agitation, coma, and slowing of the central nervous system.  Cannabis use in children (usually inadvertent) is of particular concern as children have the potential for severe toxicity, including coma and neurological and cardiovascular effects.

The analysis pooled the results of 30 studies, including ten abstracts from major clinical toxicology conferences.  The studies reported a general rise in the rate of cannabis poisoning after cannabis legalisation or decriminalisation. However, results among the studies are highly heterogenous, and most of the evidence comes from the USA and Canada, which might not apply in other countries that have legalised or decriminalised cannabis.  Studies that focused on the medical use of cannabis reported a higher risk of poisoning and were less heterogenous than those that included the recreational use of cannabis. Studies that did not report a statistically significant change for overall poisoning often found increases among subgroups, such as children or intensive care admissions.

Senior author Dr. Rose Cairns, from the University of Sydney, says, “Although the results of the studies are varied, almost all of them point to an increase in cannabis poisoning following a change to cannabis laws. The likely explanation is that legislation has increased the use of cannabis, which has also increased poisoning. For example, the modification of cannabis laws could have increased the perceived acceptability of cannabis use (if it’s legal, it must be safe), thereby increasing use.

“Increased availability and use of edibles (gummies and chocolates, for example) appears to be an important driver of the increase in poisonings, particularly among children. Edible cannabis has a higher risk of poisoning because people tend to consume larger quantities, and the effects of cannabis take longer to show up when ingested than they do when smoked.  This is concerning because edibles are especially attractive to children.”

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For editors:

This paper is available Open Access from the Wiley Online Library: or by contacting Jean O’Reilly, Editorial Manager, Addiction,

To speak with co-author Professor Nicholas Buckley please contact him via Michelle Blowes, University of Sydney Media and PR Adviser, by email ( or mobile (+61 (0)478 303 173).

Full citation for article: Allaf S, Lim JS, Buckley NA, and Cairns R. The Impact of Cannabis Legalisation and Decriminalisation on Acute Poisoning: A Systematic Review. Addiction. 2023. DOI: 10.1111/add.16280

Funding: Rose Cairns is supported by an NHMRC Investigator Grant (ID: 1196516), Nicholas Buckley is supported by an NHMRC investigator Grant (ID: 2007726).

Declaration of interests:  None.

Addiction is a monthly international scientific journal publishing peer-reviewed research reports on alcohol, substances, tobacco, and gambling as well as editorials and other debate pieces. Owned by the Society for the Study of Addiction, it has been in continuous publication since 1884.

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