A new study published in the Journal of Psychopharmacology has shed light on the potential impact of cannabis use on the cognitive abilities of adolescents with bipolar disorder. Researchers found that adolescents with bipolar disorder who had used cannabis exhibited working memory deficits compared to their counterparts who had not used the drug.
Bipolar disorder is a severe and persistent psychiatric illness that affects millions of people worldwide. It is characterized by recurrent mood episodes of depression and mania or hypomania. What makes bipolar disorder even more challenging is its high prevalence among adolescents, affecting approximately 2%–5% of this age group.
Adding to the complexity, many adolescents with bipolar disorder also struggle with substance use disorders, with cannabis being one of the most commonly used drugs alongside alcohol. Understanding the potential consequences of cannabis use in adolescents with bipolar disorder is particularly timely and crucial, given the recent legalization of cannabis in various regions.
Prior research has shown that neurocognitive dysfunction is a significant contributor to the disability and functional impairment associated with bipolar disorder. Adolescents with bipolar disorder often face challenges in areas such as verbal learning, memory, working memory, and attention. At the same time, cannabis use has been linked to cognitive deficits in adolescents. However, the specific relationship between cannabis use and neurocognition in adolescents with bipolar disorder remained largely unexplored.
“Teens with bipolar disorder are at greatly increased risk of substance use disorders,” said study author Alysha A. Sultan (@AlyshaSultan), a postdoctoral fellow at the Centre for Youth Bipolar Disorder (CYBD) located at the Centre for Addiction and Mental Health.
“One in 3 teens with bipolar disorder have a substance use disorder, with cannabis use disorder being most common. Recent changes in cannabis legislation have led to a decrease in the perceptions of harms associated with cannabis, as well as an increase in availability and acceptance of cannabis use. Therefore, understanding potential risks associated with cannabis use, particularly in teens with bipolar disorder, is of great importance.”
The study enrolled a total of 121 English-speaking participants aged 14–20 years. They were divided into three groups: those with Bipolar Disorder and lifetime cannabis use (BDCB+), those with Bipolar Disorder and no lifetime cannabis use (BDCB−), and healthy control adolescents with no history of cannabis use.
Adolescents with B were recruited from a clinical research program in Toronto, Canada, specializing in the treatment of mental health disorders. Meanwhile, healthy control adolescents were recruited through community advertisements.
Psychiatric diagnoses and cannabis use assessments were conducted using the Kiddie Schedule for Affective Disorders and Schizophrenia for School-Age Children, Present and Lifetime Version (KSADS-PL), a semi-structured interview completed by both participants and parents or guardians. The researchers collected data on various clinical and demographic factors, including mood symptoms, age of bipolar disorder onset, psychiatric hospitalizations, substance use disorders, and lifetime history of physical and/or sexual abuse.
Neurocognitive testing was carried out using the Cambridge Neuropsychological Tests Automated Battery (CANTAB), a computerized battery of tests assessing different cognitive domains.
Adolescents with bipolar disorder who had used cannabis (BDCB+) demonstrated significantly worse working memory when compared to healthy controls. Even when individuals with cannabis use disorder were excluded, the deficits remained, suggesting that cognitive impairments are observed across a range of cannabis use.
“The findings from this study suggest that cannabis use among teens with bipolar disorder is associated with working memory deficits,” Sultan told PsyPost. “Our group has also examined brain structure and function in a similar sample of teens with bipolar disorder. These papers have shown that cannabis use is associated with differences in brain structure and function in teens with bipolar disorder, as compared to teens with bipolar disorder and healthy controls who do not use cannabis.”
“These differences may contribute in part to the negative clinical correlates of cannabis use. We want to highlight the fact that risks of cannabis use are elevated in teens vs. adults in general, and that any cannabis-related consequences have the potential to be particularly harmful in teens with bipolar disorder specifically.”
The study has some limitations that should be considered. It followed a cross-sectional design, which means that it cannot establish causal relationships. Further research should explore whether the observed associations are a result of cannabis use or pre-existing factors.
The relatively small sample size limited the ability to detect small effect sizes or conduct multivariable analyses that consider other factors related to cannabis use, such as alcohol use or smoking. Future studies with larger samples may provide more comprehensive insights.
“This study was the first study to examine neurocognition in teens with bipolar disorder and cannabis use,” Sultan said. “The study sample was relatively small, and the cannabis use group reflected a wide range of use from infrequent social use to cannabis use disorder. This topic would benefit from future research using larger sample sizes, and additional information regarding cannabis including potency, frequency, amount, and duration of use.”
“We also need prospective studies with repeated measurements, in order to learn more about the timing of cannabis use in relation to mood, neurocognition, and brain imaging findings. These prospective studies would provide insights about whether the differences in neurocognition and neuroimaging measures are the outcome of cannabis use and/or whether they reflect predisposition to cannabis use.”
The study, “Association of cannabis use with neurocognition in adolescents with bipolar disorder“, was authored by Alysha A Sultan, Megan Mio, Mikaela K Dimick, Yi Zou, Sudhir Karthikeyan, Nathan Kolla, Krista Lanctot, Martin Zack, and Benjamin I Goldstein.
