Doctors have raised growing concerns about rising rates of cannabis-related psychosis .
Authors
- Myfanwy Graham
NHMRC Postgraduate Scholar and Fulbright Alumna in Public Health Policy, Monash University
- Suzanne Nielsen
Professor and Deputy Director, Monash Addiction Research Centre, Monash University
Our new ten-year study shows those concerns are well founded.
We looked at almost 40,000 cannabis-related hospital admissions in Victoria between 2013 and 2023. Over that time, cases where cannabis was the main reason someone ended up in hospital increased by 49%.
Psychotic disorder (commonly called psychosis) was the leading cause.
What we did and what we found
We examined hospital records for 39,565 cannabis-related hospital admissions in Victoria over the ten-year period.
Admissions peaked during the COVID pandemic in 2020 and 2021. Cannabis-related psychosis was the main driver across the decade, accounting for 40.1% of hospitalisations where cannabis was the main reason. Poisoning made up less than 12% of cases.
These weren’t quick visits. Most patients (68%) stayed in hospital for longer than 24 hours, with the average stay lasting a week for all cases involving cannabis. This suggests these cases were serious. More than 1,500 people required admission to an intensive care unit (ICU).
Males aged 15-24 still represent the largest total group hospitalised. But our study showed the largest increase over the decade was in younger women and adults aged 65 and older.
What can explain the findings?
During 2020 and 2021, isolation, job losses and broader mental health struggles may have contributed to many people using more cannabis.
Wastewater monitoring confirmed a rise in cannabis use around this time. Unlike some illicit supply chains disrupted by border closures, local cannabis supply remained largely accessible .
Demographics in cannabis use are shifting too. The proportion of people who have ever used cannabis has risen over the decade. More women are also using cannabis in high-risk ways, including frequent use, which may increase the risk of cannabis dependence.
Changing social perceptions may play a role. As cannabis becomes more acceptable, people may simply feel more comfortable telling doctors about their cannabis use.
Higher-strength cannabis is also likely to play role. We are seeing severe psychiatric and respiratory reactions with products containing higher levels of tetrahydrocannabinol (or THC). That’s the component that can cause drowsiness or a high.
Is medicinal cannabis to blame?
It is hard to know if prescribed medicinal cannabis or illicit cannabis explains this increase in hospitalisations. Hospital coding systems – used in health records and in the data we examined – rarely distinguish between legal (prescribed) and illicit cannabis use; many people use both .
Fewer Australians take prescribed compared to illicit cannabis. Even then, legal products come with risks.
Higher-potency products that can be inhaled are generally not recommended for safety reasons. But these are some of the most frequently prescribed products, with some containing up to 88% THC .
High-volume telehealth clinics that don’t properly screen people for existing mental health conditions or other risk factors before prescribing high-strength cannabis may also be contributing to the rise in severe mental health adverse events.
Without proper clinical monitoring, risks may not be detected, or will be detected later, and harms may be more severe by the time problems are identified.
There are wider issues
This isn’t just a Victorian issue. In fact, some studies suggest other states have higher rates of cannabis use.
Nationally, cannabis remains one of the top illicit drugs leading to a hospital admission , outpacing illicit opioids.
International data shows a similar trend. When legal access expands via profit-driven commercial models, cannabis-related psychosis hospitalisations tend to rise .
Our findings that the largest increase in cannabis-related hospitalisations was in younger women and older adults has wider implications.
Public health initiatives don’t necessarily focus on these groups. By identifying who is most vulnerable, we have an opportunity to tailor prevention campaigns, improve clinical screening before cannabis is prescribed and more broadly for vulnerable groups, and ensure safety regulations keep pace with changing products and increased availability.
