But while many may no longer see cannabis as a risky or harmful substance, there are still many things experts do not know about cannabis – including why some people develop schizophrenia after use.
Until now, most evidence has suggested that any link between cannabis and developing schizophrenia is due to using it frequently and at high dosages or that genetic predisposition may be a factor – as might a family history of schizophrenia.
To better understand whether or not frequent cannabis use increases risk of adolescents developing schizophrenia, the researchers looked at all material published on the topic between 2010 and 2020 – including studies that previous reviews on the subject had failed to include.
They found that both high and low-frequency cannabis users were six times more likely to develop schizophrenia compared to those who had never used cannabis.
But while they were able to confirm the link between any cannabis use and schizophrenia, there are still some important limitations of this study to note.
And as with other drugs, cannabis also varies in potency – and the stronger it is, the greater the risk of a person developing problems, such as schizophrenia, even if their use is not very frequent.
Although it can occur at any age, on average it tends to happen in the late teens and early 20s for men, and late 20s and early 30s for women.
Some research has also suggested that people who have a greater genetic predisposition to developing schizophrenia may also be more likely to use cannabis.
One estimate even suggests we would need to prevent 10,500 young people from using cannabis to prevent one case of schizophrenia – further showing how ineffective any public health strategy would likely be.
The incidence of schizophrenia in the general population is around one in 300 people – while those who use cannabis have at least a threefold greater risk of developing schizophrenia, making this approximately a one-in-a-hundred risk.
While perceptions of cannabis’s safety have changed in recent years – especially with many countries legalising it for use – it is still important that people think carefully about their risks before using cannabis.