Cannabis use linked to earlier psychosis, and it's not just in young people
By Olivia Henry, the Australian Science Media Centre
People who use cannabis are developing psychosis years earlier than non-users, and it’s not just young people at risk, according to Aussie researchers who are urging for greater health warnings about one of the nation’s most widely used drugs.
The analysis, which was published this week in Biological Psychiatry, looked at 149 studies involving more than 71,000 people largely across Europe, North America, and Australia since 2011, mostly focusing on people with schizophrenia.
Previous research had already established links between cannabis use and psychosis, but the researchers say their most striking finding were the ages of onset – with no evidence that cannabis users saw earlier onset of psychosis in those under 20.
Meanwhile, cannabis users aged 25 to 29 developed psychosis nearly four and a half years earlier, on average, than non-users.
The effect was even more pronounced in over 30s – with this age group developing psychosis nearly six and a half years earlier than non-cannabis users.
Carly Stevens, a trainee doctor from the University of New South Wales and the lead author of the study, told the AusSMC in a briefing earlier this week their study busts the prevailing myth that cannabis is safer to use once a person’s brain has finished developing.
"There seems to be this predominant idea of the adolescent brain being very vulnerable, which is true," she said.
“I even spoke to a doctor one time who told me that they waited until their brain had developed, which is apparently around the age of 25, before trying cannabis because they thought that it was a safe thing to do beyond that point.”
The team says there could be a few reasons for their findings, including a genetic component, or a biological “floor effect”, as UNSW’s Professor Matthew Large, who was also involved in the study, explained: “There may be a biological floor, in that there is only so much earlier that onset can be shifted.”
“In younger groups, strong development, genetic or other psychosis risk factors may dominate, making any cannabis-related age shift harder to detect,” he said.
The findings also point towards a possibility that cannabis is a “cumulative neurotoxin” – something that builds up over time, and mostly shows negative effects after long exposure and use.
While the researchers acknowledge there are some cases where cannabis has been shown to be effective for medical reasons – such as weight loss associated with HIV, and rare infantile epilepsy, they say that many of the most common reasons for prescribing cannabis are not supported by evidence.
“Common indications are pain, anxiety, depression, and insomnia, all of which are either worsened or not helped by cannabinoids,” Professor Large said.
While the research did not look specifically at legislation in Australia, the team say from their perspective, Australia needs better education and public health messaging on cannabis, both for the public and for prescribers.
“At the moment the way that this is being handled is quite inappropriate,” Ms Stevens said.
Ms Stevens said currently in Australia, the only two ways to obtain cannabis are illegally (through a drug dealer) or through the medical pathway.
If there were a third way to obtain cannabis, Ms Stevens added, Australia could then provide health warnings and information about when cannabis use is medically appropriate, and what risks and harms users must consider.
Recreational cannabis use could also then be taxed, with that money being used to fund healthcare relating to cannabis-related harms.
“People should have access to a subsidised medication to alleviate suffering,” she said.
“But for the people that would prefer to just use it recreationally. We should treat it for what it is, which is for them a recreational substance that's associated with significant harms.”
Dr Large agreed, adding that he thinks the medicalisation of cannabis has halted conversations about cannabis toxicity – with detrimental effects.
"It's that part of public policy that I think will quite likely prove to be one of the biggest public health bungles in Australian history,” he said.
Read more about the AusSMC briefing here
This article originally appeared in Science Deadline, a weekly newsletter from the AusSMC. You are free to republish this story, in full, with appropriate credit.
Contact: Olivia Henry
Phone: +61 8 7120 8666
Email: info@smc.org.au