An archival review of young patients referred to Alberta Hospital Edmonton's Neuropsychology unit shows that cannabis use had no positive impact on cognitive impairment in psychosis, but was associated with lower estimated IQ levels prior to the onset of a primary psychotic disorder.
Those were among the findings of a study by Dr. Scot Purdon, a Clinical Neuropsychologist at AHE, and Dr. Kim Goodard, a Clinical Neuropsychologist at Calgary South Hospital. They examined the records for over a hundred patients referred for assessment between December 2001 and March 2012.
Dr. Purdon, a Clinical Professor in the Department of Psychiatry and Director of the Bebensee Schizophrenia Research Unit, presented highlights of his findings on the Clinical Neuropsychological effects of Cannabis at a research symposium Oct. 9th.
The sale of recreational cannabis was legalized in Canada by the federal government on Oct. 17th.
The Symposium on Cannabis, Endocannabinoids & Mental Health, sponsored by the Department of Psychiatry's Neurochemical Research Unit and the Neuroscience and Mental Health Institute, was held at the Lister Centre.
Dr. Purdon was one of eight experts in the field of cannabis research and policy from the University of Alberta, the University of Calgary and Alberta Health Services who presented to the symposium.
"The first question I was interested in was really motivated by a meta-analysis suggesting cognitive benefits of cannabis use on cognition in psychosis. The authors came up with a list of pros and cons - good things and bad things about cannabis - and remarkably, psychosis was on both lists, apparently exacerbating symptoms of psychosis but potentially improving cognition," Dr. Purdon told attendees.
"I've been working with Schizophrenia for almost 40 years now and I've not noticed cognitive benefits associated with cannabis use in this population. I'm not so sure that could be true. So I dug into the literature …. and the one thing that jumped out at me was that the studies that were cited did not explicitly separate out people with a substance-induced psychosis from people with a primary psychotic illness, like Schizophrenia."
Although consumption of cannabis produces a temporary "psychotic like" experience, it is fundamentally different from a neurodevelopmental pathology that causes psychosis, he noted.
"The hypothesis we had was, if we separate out a substance-induced psychosis group from a group with a primary psychotic illness, the primary psychotic illness group will perform worse than the substance-induced psychosis group - similar to the published results suggesting cannabis users with psychosis might perform better than non-users with psychosis," he told the symposium.
"The second (hypothesis) was, if we pull out the primary psychosis group, and look at those who use cannabis, they should do worse - not better - than people with a primary psychotic disorder who do not use cannabis - contrary to the published literature," he added.
The researchers found that both the substance-induced psychosis patients and those patients with a primary psychotic disorder showed cognitive impairments, but the impairment was more severe among those with a primary psychotic disorder. They also found that cannabis users with a primary psychotic disorder performed worse than non-cannabis users with a disorder, on measures of memory and verbal learning.
"If you have a psychotic disorder, a primary psychotic disorder and you use cannabis, your cognitive function will not be as good as if you do not use cannabis," he said.
"To sum up, I went looking for the beneficial effect of cannabis in psychosis. I did not find a beneficial effect of cannabis in psychosis. I did find a methodological artifact in the classification of patients with primary psychosis versus substance-induced psychosis that could explain the previous anomalous results," he said.
"It will be very important I think to future research in this area. If you have a psychotic disorder, a primary psychotic disorder and you use cannabis your cognitive function will not be as good as if you do not use cannabis. In fact, earlier use of cannabis seems to be associated with lower pre-morbid IQ."
Those were among the findings of a study by Dr. Scot Purdon, a Clinical Neuropsychologist at AHE, and Dr. Kim Goodard, a Clinical Neuropsychologist at Calgary South Hospital. They examined the records for over a hundred patients referred for assessment between December 2001 and March 2012.
Dr. Purdon, a Clinical Professor in the Department of Psychiatry and Director of the Bebensee Schizophrenia Research Unit, presented highlights of his findings on the Clinical Neuropsychological effects of Cannabis at a research symposium Oct. 9th.
The sale of recreational cannabis was legalized in Canada by the federal government on Oct. 17th.
The Symposium on Cannabis, Endocannabinoids & Mental Health, sponsored by the Department of Psychiatry's Neurochemical Research Unit and the Neuroscience and Mental Health Institute, was held at the Lister Centre.
Dr. Purdon was one of eight experts in the field of cannabis research and policy from the University of Alberta, the University of Calgary and Alberta Health Services who presented to the symposium.
"The first question I was interested in was really motivated by a meta-analysis suggesting cognitive benefits of cannabis use on cognition in psychosis. The authors came up with a list of pros and cons - good things and bad things about cannabis - and remarkably, psychosis was on both lists, apparently exacerbating symptoms of psychosis but potentially improving cognition," Dr. Purdon told attendees.
"I've been working with Schizophrenia for almost 40 years now and I've not noticed cognitive benefits associated with cannabis use in this population. I'm not so sure that could be true. So I dug into the literature …. and the one thing that jumped out at me was that the studies that were cited did not explicitly separate out people with a substance-induced psychosis from people with a primary psychotic illness, like Schizophrenia."
Although consumption of cannabis produces a temporary "psychotic like" experience, it is fundamentally different from a neurodevelopmental pathology that causes psychosis, he noted.
"The hypothesis we had was, if we separate out a substance-induced psychosis group from a group with a primary psychotic illness, the primary psychotic illness group will perform worse than the substance-induced psychosis group - similar to the published results suggesting cannabis users with psychosis might perform better than non-users with psychosis," he told the symposium.
"The second (hypothesis) was, if we pull out the primary psychosis group, and look at those who use cannabis, they should do worse - not better - than people with a primary psychotic disorder who do not use cannabis - contrary to the published literature," he added.
The researchers found that both the substance-induced psychosis patients and those patients with a primary psychotic disorder showed cognitive impairments, but the impairment was more severe among those with a primary psychotic disorder. They also found that cannabis users with a primary psychotic disorder performed worse than non-cannabis users with a disorder, on measures of memory and verbal learning.
"If you have a psychotic disorder, a primary psychotic disorder and you use cannabis, your cognitive function will not be as good as if you do not use cannabis," he said.
"To sum up, I went looking for the beneficial effect of cannabis in psychosis. I did not find a beneficial effect of cannabis in psychosis. I did find a methodological artifact in the classification of patients with primary psychosis versus substance-induced psychosis that could explain the previous anomalous results," he said.
"It will be very important I think to future research in this area. If you have a psychotic disorder, a primary psychotic disorder and you use cannabis your cognitive function will not be as good as if you do not use cannabis. In fact, earlier use of cannabis seems to be associated with lower pre-morbid IQ."