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Quitting cannabis use improves cognition in people with schizophrenia

​CAMH study’s findings may point to a new approach to benefit the high proportion of people with schizophrenia who also have a cannabis use disorder

TORONTO, June 29, 2017 - A new CAMH study suggests that quitting cannabis substantially improved an important aspect of cognition in people with schizophrenia who were chronic cannabis users. Published in April 2017 in Neuropsychopharmacology, it’s the first study to investigate how abstaining from cannabis use for one month impacts cognition or thinking processes in this population.

About one in every 100 people has schizophrenia, a complex and severe mental illness. People with schizophrenia may experience impairments in cognition that profoundly affect everyday living, says Dr. Tony George, senior author of the study and Chief of CAMH’s Addiction Division. Cognition refers to the thinking processes involved in learning, memory and applying knowledge.

Dr. Tony George
Dr. Tony George

High rates of cannabis use among people with schizophrenia and poor outcomes related to its use interested the research team in studying how cannabis abstinence alters cognition, says Dr. George. While about three per cent of the general population has a cannabis use disorder, the rate soars dramatically in people with schizophrenia – it’s estimated that about 25 per cent of people with schizophrenia also have a cannabis use disorder.

The preliminary study, led by Dr. Rachel Rabin while completing her Ph.D. studies, looked at how quitting cannabis use for 28 days affected several areas of cognition, including verbal learning and memory, attention, impulsive behaviours and motor function. A total of 19 people with schizophrenia and a comparison group of 20 people without a mental illness, all of whom had cannabis dependence, attempted to abstain from cannabis use for the full study period. In people with schizophrenia, the area called verbal learning and memory improved significantly – by 40 per cent by the study’s end.

“In people with schizophrenia, our research showed that if you can abstain, you will see better outcomes in a key area of cognition,” says Dr. George, who also heads the Biobehavioural Addictions and Concurrent Disorders Research Laboratory in CAMH’s Campbell Family Mental Health Research Institute, and is Professor of Psychiatry at the University of Toronto.

Verbal learning and memory is the ability to understand and recall what we’ve heard, and it’s vital to everyday living, allowing us to remember a conversation, directions or other information that people share orally. In earlier research, it’s also been shown to be impaired in both people with schizophrenia and individuals with cannabis use disorder. Improving verbal learning and memory could make a marked difference in a person’s life, such as helping a person to succeed in the workplace, says Dr. George.

Ranging from ages 18 to 55, participants were asked to quit using cannabis for 28 consecutive days, the period needed for this long-acting substance to be fully out of a person’s body, and received counselling to help manage withdrawal symptoms and cravings. By the end of 28 days, eight of 19 people with schizophrenia and 11 of 20 people from the comparison group had abstained from cannabis use for the full study period. “These abstinence rates illustrate the difficulties that people frequently experience when attempting to quit chronic cannabis use,” says Dr. George.

Researchers assessed different aspects of cognition during and at the end of the study. While verbal learning and memory improved significantly in people with schizophrenia, people in the comparison group experienced only a minor improvement, which supports early findings that people with schizophrenia may be more susceptible to the effects of cannabis use.

“As we approach cannabis legalization in Canada, our study provides further evidence that, in people with mental illness, cannabis use warrants caution,” says Dr. George. The research team will look to investigate cannabis abstinence further in this population in a larger sample.

The study was supported by the Canadian Institutes of Health Research, the Brain and Behavior Research Foundation and the Chair in Addiction Psychiatry at the University of Toronto.

Given the challenges associated with quitting chronic cannabis use, Dr. George and CAMH Scientist Dr. Mera Barr are both leading studies using a novel, non-invasive brain stimulation treatment, called repetitive transcranial magnetic stimulation (rTMS). “There are no medications to treat cannabis use disorder – the only treatments are behavioural therapies provided by a health-care professional,” says Dr. George. “Our goal is to determine if brain stimulation can help reduce the cravings people have when they experience cannabis withdrawal, which play a big role in people relapsing.” In an earlier study, Dr. George showed that rTMS reduced cigarette cravings in smokers with schizophrenia.

The Centre for Addiction and Mental Health (CAMH) is Canada’s largest mental health and addiction teaching hospital and a world-leading research centre in this field. CAMH combines clinical care, research, education, policy development and health promotion to help transform the lives of people affected by mental illness and addiction. CAMH is fully affiliated with the University of Toronto, and is a Pan American Health Organization/World Health Organization Collaborating Centre. For more information, please follow @CAMHnews or @CAMHResearch on Twitter.

For more information, please contact:

Sean O’Malley
Media Relations, CAMH
(416) 595-6015 / media@camh.ca

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