Cannabis use rarely increases the risk of psychosis, according to a new study from a scientist at the University of York.
The risk of developing psychosis from cannabis use is relatively small, according to a new study published in the journal Addiction. The research review, conducted by Dr. Ian Hamilton of the University of York’s Department of Health Services, found evidence that about 23,000 people would have to stop using cannabis to prevent just one case of psychosis.
According to the study, the greatest risk to health with cannabis use comes from combining it with tobacco. Unlike in the U.S., where people tend to use cannabis on its own, it’s common in the UK to use marijuana with tobacco. Young people who become dependent on tobacco early on were found to have an increased risk of cancers, infections, and other health issues.
While evidence shows that those vulnerable to developing mental health problems with cannabis use are rare, Hamilton did note that most of the studies he investigated are decades old.
“The link between cannabis and psychosis has been an ongoing research topic since the drug became popular in the 1960s,” Hamilton said. “Most of the high profile studies that we have access to, however, are from a time when low potency cannabis was the norm, but today high potency is more common.”
The levels of tetrahydrocannabinol (THC) found in some cannabis strains today are higher than when most of the studies included in Hamilton’s review were completed. He urged for more research on the effects of high-THC strains.
“Higher potency cannabis contains … higher levels of tetrahydrocannabinol (THC) which can trigger psychosis,” Hamilton told The Independent.
“In this new study, we looked at both low and high potency, but it is clear that we need more evidence from high potency-related health cases to further investigate this link in modern-day users,” he said.
Hamilton says that his findings suggest that prohibition isn’t an effective method for managing public health concerns as banning would have low impact on mental health. Legalizing and regulating marijuana would implement quality and safety standards on cannabis products, he argues, and give users more information on what they’re consuming.
“Regulation could help reduce the risks to health that cannabis use poses, and as a regulated cannabis market would introduce some quality control,” he said. “This would provide users with information about the strength of cannabis on offer, something they usually only discover after exposure in the current unregulated market.”
“The public health message about the link between cannabis and psychosis has been a difficult one to communicate, but the evidence still points to the benefits of regulations that seek to advise on the greatest potential health risks, which currently arise due to tobacco use.”
Hamilton did find sufficient evidence indicating that cannabis can make symptoms worse for patients who already have schizophrenia. Also, heavy users were more likely to experience mental health problems.
You can access Hamilton’s entire study, “Cannabis, psychosis and schizophrenia: unraveling a complex interaction,” via Wiley Online Library.