source : the age
When Patrick Leunig finished high school with a great ATAR and a coveted spot in a law degree, his father assumed he was on the path to success.
“It looked like he had his whole future in front of him,” Patrick’s father, Andrew Leunig, said.
“We later found out he started smoking cannabis in Year 11, when he was 16.”
Patrick dropped out of university inside a year. By the time he was 21, he was hospitalised against his will for the first time, when the delusions and conspiracies of drug-induced psychosis made it clear he needed help.
In April 2024, Patrick was found dead of a methamphetamine overdose. It was two days before his 26th birthday.
“If he had never smoked cannabis, would he have had a mental illness? I don’t know the answer,” Leunig said.
A landmark Australian-led global study found cannabis users develop psychosis an average two-and-a-half years earlier than non-users who experience psychosis.
The largest study of its kind, published in Biological Psychiatry, involving 149 studies with data from more than 70,000 individuals, found that the younger people started smoking cannabis, the worse the clinical outcomes. They lost years of healthy life and incurred greater healthcare and societal costs.
Cannabis users in their early 20s developed psychosis 1.6 years earlier than non-users, while those over 30 developed psychoses about 6.3 years earlier, the analysis found.
University of NSW professor of psychiatry Matthew Large, one of the study’s co-authors, said the most plausible explanation is the increased years of exposure.
The cumulative toxicity of cannabis was comparable to lung cancer and tobacco – the longer someone smokes, the higher their risk, Large said.
Co-author Carly Stevens said there was a prevailing myth that “you’ll be fine if you wait to smoke weed until your mid-20s,” once your brain had developed.
“What we’ve found challenges the assumption,” she said. “There’s been so much emphasis on adolescents not smoking cannabis, which is important, but we need to broaden the warnings for everyone … no one is really safe when it comes to trying cannabis.”
Cannabis users are two to five times more likely to develop schizophrenia, with a six-year average delay between initial cannabis use and the onset of psychosis.
Medicinal cannabis has surged in popularity since its introduction in 2016, as outlined by Penington Institute reports. In 2025, 6.35 million units of the prescription drug were sold in Australia, a 279 per cent increase in three years, with 1.68 million units sold in 2022.
Medicinal cannabis is essentially identical to illicit cannabis, Large said, and carries the same or greater risk, given it tends to have a higher concentration of THC.
“I think we have effectively legalised cannabis already, but we’ve given it a halo of a medicine that has meant that it’s very difficult to talk about its harms,” he said.
“You can buy it with almost no information about how bad it may be for you. I think we’ve just ended up with the worst of both worlds.”
Studies have found no evidence that medicinal cannabis is effective for treating anxiety, depression and PTSD.
The Australian Institute of Health and Welfare’s 2022–2023 National Drug Strategy Household Survey found 3 per cent of Australians had used cannabis for medical purposes in the previous 12 months, equating to about 700,000 people.
Dr Pramudie Gunaratne, CEO of the Australian Society of Psychiatrists, said prescribing doctors had a responsibility to ensure patients understand the risks of psychosis: “The growth of medicinal cannabis has been incredibly rapid, but our understanding and communication of the psychiatric risks hasn’t kept pace.
“Cannabis has become increasingly normalised as both a recreational drug and a medicine. This study is an important reminder that normalisation doesn’t make it harmless,” she said.
Leunig said there was no known history of psychosis in his family, and Patrick’s “rolling chaos” was eventually diagnosed as schizoaffective disorder, with his initial cannabis dependency a clear “gateway drug” to meth use.
“Patrick was generally a pretty happy, healthy kid … to then become very unwell and continue to be unwell, it was just horrible.”
Leunig can’t help thinking that Patrick’s life would have been different had he developed psychosis later in life.
“If you’re a bit older and more established, you have more resilience, you’d have some experience of being an adult, before the onset of illness,” he said.
“I certainly underappreciated the risks of cannabis, [and] I think most people would not be aware of how dangerous it can be for vulnerable people.”
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