People who use cannabis alone rather than with others are twice as likely to screen positive for psychosis, a new Dalhousie University study has found.

The study, published last month in Drug and Alcohol Review, also found that solitary tokers are more likely to use the drug more often, to have symptoms of cannabis dependence and to use it to cope with negative emotions or stress.

Toni Spinella, a master's student in psychology and neuroscience and the study's lead author, said she and the team of researchers wanted to explore whether some of the harms of cannabis use are connected to solitary versus social use.

"I think it's helpful to see if this social context should be something that we should be targeting in prevention and harm reduction programs in the future," Spinella said. "So, should we be telling youth or adults or anyone who is using cannabis, 'OK, maybe you should use with other people or maybe you should use alone?'"

The researchers crunched the numbers from interviews conducted at Dalhousie in 2011 with 188 adults in Halifax. The participants, who ranged in age from 18 to 59, were asked about the last time they used cannabis as well as questions related to psychiatric symptoms. Forty-four per cent of those interviewed were women.

Toni Spinella is a master's student in psychology and neuroscience at Dalhousie University and the lead author of a recently published study on cannabis use. (Submitted by Toni Spinella)

Spinella is quick to point out that the results of the study do not point to cause and effect — so, for example, the study does not suggest that using cannabis alone causes psychosis.

"It just means they're more likely to qualify for that diagnosis if they were actually given a diagnostic questionnaire or a test," Spinella said.

There was no significant correlation between the social context of cannabis use and other psychiatric disorders such as depression, post-traumatic stress, panic and social anxiety disorders.

Using cannabis to cope

People who last used cannabis alone reported using it more often — on average 25 days out of the previous 30 days, as opposed to 12 days out of 30 for those whose last use was with others.

Spinella said that finding, along with the discovery that solitary users were more likely to have dependence symptoms and more likely to consume marijuana as a coping mechanism, could be a concern for those users.

"It's possible that they lack other coping strategies," she said. "If you're alone, why are you using alone? That's something that you might want to ask yourself and if you realize, 'OK, I'm using alone because I'm sad tonight or I'm stressed,' then maybe that's a red flag that you should think more about."

One surprise among the study's findings, Spinella said, was that those who got high with others were almost three times as likely to consume alcohol at the same time.

"But it does make sense … because if you think of social and contextual factors — for example peer influence, if you go to a party and there's people drinking around you there's alcohol cues everywhere, people are intoxicated, you smell it in the air, there's music — you're also more likely to drink."

More research needed

Zach Walsh is an associate professor of psychology at the University of British Columbia who specializes in the study of cannabis and psychedelics. He was not involved in the study.

Like Spinella, he cautioned that the study does not point to a causal relationship between cannabis use and the patterns identified in the study.

But he said it is a "small but notable contribution" to the field of cannabis research and that social context of cannabis use warrants more study.

"Set and setting is very important. So I really applaud the authors' decision to take a good look at the influence of context," he said.

The study notes that reliance on participants' memories could affect the quality of the data. For that reason, researchers focused only on the participants' most recent occasion of cannabis use in order to improve accuracy. However, the paper acknowledges that not be representative of a user's typical consumption pattern.

Spinella said the findings of her study should be explored through further research.

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