Cognitive function among people with severe substance use.

Introduction: Studies report a high variability of cognitive impairment in people who use drugs, ranging from 20% to 80%. Most research focus on individuals who use drugs who are either admitted to treatment facilities or incarcerated and being abstinent from substances. The present study aimed to assess cognitive function among populations with ongoing, severe, habitual substance use, mimicking a real-world day-to-day situation.

Methods: Cross-sectional design with 171 participants (70.2% male) with severe substance use, recruited from two sites in Oslo, Norway. All participants were screened for cognitive function using the Montreal Cognitive Assessment (MoCA). A cutoff of < 26 points was used to classify possible cognitive impairment. Participants also provided information on their alcohol and substance use, as well as demographic data.

Results: 74.9% of the participants scored below the MoCA cutoff for possible cognitive impairment. We did not find any associations between scoring below the MoCA cutoff <26 and the substance use variables (substance use, number of substances used, history of overdoses, injection drug use, and past substance use treatment).

Conclusion: A high proportion of people with severe substance use may experience a functional cognitive impairment. This study provides novel insights into cognitive function within a population actively engaged in habitual substance use, offering a real-world perspective with high external validity. This knowledge is highly relevant for service providers who aim to deliver tailored follow-up services to this population outside of traditional treatment settings.