For people at risk of psychosis, cannabis use can be dangerous

Strong evidence connects cannabis use as a teenager (especially before the age of 16) to worsening symptoms of psychosis. For some young people, the first visit to the emergency room for cannabis-induced psychosis can lead to schizophrenia within three years.

In both schizophrenia and frequent cannabis use, the brain’s synaptic density—its connectivity—is reduced. If a youth is already at risk of psychosis—displaying emergent psychotic symptoms such as irritability, suspiciousness, low mood, and other changes in their behaviour and perceptions of things around them—cannabis use exacerbates the existing issue.

“We wanted to understand the contribution of cannabis use in these brain connections. We showed that early psychosis patients and those at risk for psychosis had lower synaptic density. Synaptic density was also lower in cannabis users” says Dr. Romina Mizrahi, senior author of the study, who has spent two decades researching the impact of cannabis use on the brain.

Dr. Mizrahi recruits young people, mostly in their early twenties, who have come to the Douglas Mental Health University Institute in Montreal experiencing emergent symptoms of psychosis—starting to hear voices or see things that aren’t there, or beginning to believe someone is watching them. Many of these individuals seek help in the emergency room after experiencing symptoms for the first time.

People who started using cannabis before the age of 16 face the highest risk. This is particularly pronounced in young males, where a similar study by Dr. Daniel Myran found that 40% of men aged 16–24 were diagnosed with schizophrenia after an emergency room visit for cannabis-induced psychosis.

In total Dr. Myran’s study found that 26% of people who visited the emergency room for cannabis-induced psychosis were diagnosed with schizophrenia within three years.

“It’s important for young people to understand the potential risks,” emphasizes Dr. Mizrahi.

Lower synaptic density is associated with negative symptoms such as social withdrawal, lack of motivation, and low mood. But intervening in time can make a big difference, even improving the brain’s connectivity.

“What’s very exciting is that any psychosocial intervention which will increase social interactions and motivation may also increase synaptic density,” says Dr. Mizrahi. “This opens the door for psychosocial interventions to increase synaptic density, alongside medications.”

This groundbreaking study is the first to focus on individuals showing emergent psychotic symptoms rather than people who have already had their first psychotic episode. As such, it allows for earlier interventions and could have a bigger impact for youth at risk of psychosis, perhaps even helping prevent it.

At a glance

Issue

Both cannabis use and psychosis lower the brain’s synaptic density, or connectivity, which can result in negative symptoms like social withdrawal and lack of motivation, in addition to worsening symptoms of psychosis.

Research

Dr. Mizrahi and the team at the Douglas have established that synaptic connections are reduced early in psychosis and in the emergent psychosis phase. Synaptic connections are similarly reduced by cannabis use. Their research has also found that reduced brain connections in young people are associated with less social interactions and motivation.