Cannabis Hyperemesis Syndrome Cases Have Risen With Cannabis Commercialization, Study Finds

Emergency department visits for cannabis hyperemesis syndrome (CHS) have increased significantly since the commercialization of cannabis in Ontario, according to a new study from the Ottawa Hospital Research Institute.

Published in JAMA Network Open, the study found that legalization itself was not associated with any significant changes in CHS-related emergency department (ED) visits. However, large increases in CHS ED visits were seen shortly following the wider market commercialization in Ontario, which included the opening of more retail stores and the sale of more diverse and potent products.

In light of their findings, the researchers are calling for the further study of cannabis commercialization and its impacts on different demographics. Additionally, they advise that greater awareness of CHS among physicians could help to ensure that patients receive effective treatment and can avoid repeat ED visits.

Monthly CHS rates have increased 13-fold since 2014

CHS is a lesser-known risk of frequent, heavy cannabis use. Individuals with CHS often report having episodes of uncontrollable vomiting, accompanied by abdominal pain and a loss of appetite. Despite reports that CHS cases are on the rise in Colorado following state legalization, so far there has been minimal investigation into understanding who is at risk for developing CHS and what effect regulatory policy may have on case rates.

In this new study, the researchers examined CHS-related ED visit data in Ontario over three distinct time periods: pre-legalization (January 2014 to September 2018), legalization with restrictions on products and retail store caps (October 2018 to February 2020), and commercialization with new product types and retail expansion (March 2020 to June 2021). These healthcare data included all individuals aged 15 or over who were eligible for Ontario’s single-payer universal health insurance.

The researchers identified 12,833 ED visits for CHS from a total of 8,140 individuals over the study period. Of these, approximately 9% of visits led to hospital admissions. They also found that the monthly rates of CHS ED visits increased 13-fold over the 7.5 years studied, rising from 0.26 visits per 100,000 people in January 2014 to 3.43 visits per 100,000 people by June 2021.

Statistical analysis revealed that legalization itself was not associated with any change in ED visit rates. But once the state lifted its cap on the number of retail store locations and began to allow the sale of more potent products, including concentrates and edibles, there was an immediate increase in the rates of CHS ED visits.

Cannabis rose from being the fifth-most common co-diagnosis with vomiting pre-legalization to being the most common co-diagnosis following Ontario’s commercial market expansion. The proportion of all-cause vomiting ED visits related to cannabis use also increased nearly five-fold during the commercialization period compared to pre-legalization figures.

Using counterfactual analysis, where researchers use past data to construct a hypothetical scenario where commercialization (and the Covid-19 pandemic) did not occur, it was estimated that commercialization resulted in a net increase of 32% in the rate of CHS ED visits per capita.

Commercialization significantly impacts women and young people

Interestingly, the increase in CHS ED visit rates was not uniform across all demographic groups. While rates remained relatively stable for men and those aged 45 and older, significant net increases were seen for women and individuals aged 19 to 44. Similarly, an immediate visit-increase was seen for individuals living in the lowest income quintile, but not for those in the highest income neighborhoods. The researchers say that more research is still needed to understand why these groups may be affected differently.

The study authors do note some limitations with their work. Most notably, there is currently no official diagnostic code for CHS that is in use in Ontario healthcare records. This meant that the researchers were limited to considering ED visits where vomiting was listed as a primary diagnosis and a cannabis harm as an additional diagnosis to be a case of CHS. They estimate that this approach may undercount the real burden of CHS on the health service, as not all patients will disclose their cannabis use and physicians are generally less aware of CHS being a potential complication with heavy cannabis use.

The outbreak of the coronavirus pandemic also coincided with the timeframe of commercialization, though the researchers believe their findings are more attributable to the effects of commercialization than Covid-19.

“The overlap of the commercialization of Ontario’s cannabis retail market and the COVID-19 pandemic challenges attribution of each event to the observed increases in CHS ED visits. However, 3 points support that commercialization likely played a role. First, we observed that increases in CHS ED visits during the pandemic were much larger than changes in ED visits for mental health and substance use,” the authors wrote.

“Second, we did not observe an increase in CHS ED visits for individuals younger than the legal age of cannabis purchase in Ontario, but we did observe large increases among young adults who could access the legal market,” they continued.

“Third, the risk factor for CHS is regular use of high-potency cannabis. Sales data supports that the strength (THC content) of cannabis products has increased substantially since legalization, particularly when new products were introduced during commercialization.”

Potency restrictions may help to curb CHS cases, experts say

While previous studies, like the Colorado study, have indicated that legalization may be associated with an increase in CHS cases, the researchers behind this latest study say their results suggest this change could be significantly influenced by local regulatory approaches. Specifically, policies that restrict product variety and strength, and which place limits on the number of licensed retail stores, may counteract some of the risk factors that contribute to CHS, such as access to highly-potent cannabis products.

The lack of change among those younger than the legal cannabis use age may also suggest that setting a higher legal age of purchase could reduce the risk of CHS among youth and young adults.

Given that this study also observed a substantial number of individuals who made a repeat visit to the ED for CHS in the six months following their initial visit, the researchers say that more awareness of CHS among physicians could also be beneficial. Better recognition of CHS symptoms could help patients get a timelier diagnosis and effective treatment regimen.