Study: Cannabis ‘not associated’ with increased rates of psychosis in ‘high risk’ teenagers

In a new study, cannabis was not associated with increased rates of psychosis or other adverse health outcomes among adolescents classed as ‘high risk’ for the disorder.

Researchers at Hofstra University in New York and Stanford University in California, assessed the relationship between cannabis use and health outcomes in a group of adolescents clinically at high risk of developing psychosis. 

Participants were tracked over a two-year period during which researchers examined associations with clinical and neurocognitive outcomes, along with rates of medication use.

Their findings, published in the journal Psychiatry Research, suggest that continuous cannabis use over the follow-up period was not associated with increased rates of psychosis and did not worsen clinical symptoms, levels of functioning or overall neurocognition. 

The paper goes on to say that those who continuously used cannabis had higher neurocognition and social functioning over time, as well as decreased medication usage, compared to those who did not use cannabis. Their clinical symptoms were reported to have improved over time despite the reduction in medication.

Authors concluded: “Continuous cannabis use over 2-years of follow-up was not associated with an increased psychosis transition rate, and did not worsen clinical symptoms, functioning levels, or overall neurocognition …  indicating that CHR [clinical high risk] youngsters are not negatively impacted by cannabis.”

They add: “These findings should be confirmed in future clinical trials with larger samples of cannabis using individuals.”

Earlier this year, researchers from the UK, Europe and Australia, also examined the association between cannabis use and incidences of psychotic disorders in clinically at-risk subjects.

They reported ‘no significant association between any measure of cannabis use at baseline and either transition to psychosis, the persistence of symptoms, or functional outcomes’.

The paper concluded:  “Our primary hypothesis was that cannabis use in CHR [clinically high risk] subjects would be associated with an increased rate of later transition to psychosis. However, there was no significant association with any measure of cannabis use. … These findings are not consistent with epidemiological data linking cannabis use to an increased risk of developing psychosis.”

Cannabis, psychosis and other psychiatric disorders – a controversial topic

As cannabis becomes more widely accessible across the globe, its longstanding link to  psychosis remains a controversial topic. In reality, the research around this – as well as its association with other mental health disorders – is conflicting and there is still a lot we don’t know.

Studies published this year have found no ‘statistically significant difference’ in the rates of psychosis-related diagnoses, in US states with medical or recreational cannabis policies compared to those without.

However, in contrast to the findings above, a recent study from Spain identified an increased risk of developing a mental health disorder among young people admitted to treatment for cannabis use disorder.

While some experts argue that a causal association between cannabis use and psychosis has been identified in psychiatric epidemiology among a minority of users, others say that factors such as poverty, social deprivation and trauma make it difficult to infer a causal link with any certainty. 

That said, clinicians generally advise caution around cannabis use for anyone who has a family history of psychosis or may be predisposed to developing symptoms. 

Read more on this subject here: A conversation about cannabis and psychosis