Results from a systematic review published in Psychiatry Research outline the impact of comorbid substance use disorder (SUD) on patients with bipolar disorder. Compared to individuals without comorbid SUD, patients with bipolar disorder and SUD experienced significant impairments in cognition, executive functioning, and verbal and visual memory.
Investigators searched the PubMed, PsycINFO, and Embase databases from inception through February 2021 for studies describing the cognitive performance of patients with bipolar disorder with and without comorbid SUD. Cross-sectional and prospective cohort studies were included; reviews, meta-analyses, case reports, and conference abstracts were not. Two independent reviewers extracted study data and assessed methodological quality using the Joanna Institute critical appraisal tools.
Of 2567 studies included in the initial screening, 14 were included in the systematic review. Selected studies were published between 1998 and 2020, though the majority were published in 2010 or later. Most were conducted in the United States (n=8), though 1 each was conducted in Brazil, India, Japan, the Netherlands, Spain, and Taiwan. Studies assessed alcohol, cannabis, tobacco, and cocaine use. The most commonly used tests of cognition were the Stroop Colour and Word test and the Controlled Oral Word Association Test.
Over half of the articles (n=9; 64%) identified cognitive impairments in patients with a comorbid SUD compared to patients with bipolar disorder only. Three cross-sectional studies identified deficits in visual memory, conceptual reasoning, immediate recall, and recognition in patients with bipolar disorder and any SUD. Eight studies described the effects of alcohol use disorder specifically; 5 (62.5%) found increased cognitive impairments in the domains of verbal and visual memory in patients reporting alcohol abuse.
Alcohol use disorder in bipolar disorder was also associated with impaired executive functioning compared to bipolar disorder only. There was no consensus on the effects of cannabis and cocaine use on cognition in bipolar disorder. One study found impaired cognition in patients who reported cannabis abuse, though another study described no significant difference between groups. Tobacco smoking was associated with cognitive impairment only in patients with a history of psychosis.
Results from this review suggest that a comorbid SUD has significant effects on cognition in patients with bipolar disorder. Impairments with alcohol abuse were particularly pronounced.
Review limitations include between-study heterogeneity inpatient mood states and the lack of information on substance use frequency and amount. Further research is necessary to explore the cross-sectional and longitudinal impacts of substance abuse on patients with bipolar disorder.
“[T]his review…highlights the need for more careful future considerations of cognitive phenotype, substance use type, and pattern, and the longitudinal associations of cognitive impairment in individuals with BD and SUD,” the authors wrote. “It is important for clinicians to recognize that comorbidity of BD and SUD is associated with poorer clinical outcomes, and treatments targeting the prevention of substance use in individuals with BD are recommended.”
Gogia M, Shah AQ, Kapczinski F, de Azevedo Cardoso T. The impact of substance use disorder comorbidity on cognition of individuals with bipolar disorder: a systematic review. Psychiatry Res. Published online March 23, 2022. doi:10.1016/j.psychres.2022.114525