Working memory impairment in cannabis- and opioid-dependent adolescents

Background: Cannabis and opioid use are associated with cognitive impairment, whether preexisting or substance-induced, but there have been few substance-specific assessments of cognitive functioning in adolescent substance users. Working memory impairment may be particularly important, as it has been linked to poorer performance in substance abuse treatment.

Methods: Working memory (Wechsler Intelligence Scale for Children-IV or Adult Intelligence Scale-IV) and baseline substance use were assessed in 42 youth (mean age = 17.9 years, SD = 1.3, range: 16-20; 65% Caucasian, 30% female) 1-2 weeks after admission to residential treatment with supervised abstinence, 19 for primary cannabis dependence and 23 for primary opioid dependence.

Results: There were substantial deficits in working memory in both groups, with significant differences (P <.001) between the opioid (M = 39.1th%ile, SD = 25.6) and cannabis (M = 16.3th%ile, SD = 13.6) groups. The primary opioid group had high rates of cannabis use, with no significant difference in past-month days of cannabis use from the primary cannabis group. The opioid group was older and had completed more years of formal education. Seventy-nine percent of the cannabis group had public health care coverage (mostly Medicaid), compared with 24% of the opioid sample.

Conclusions: Working memory impairment was substantial in treatment-seeking youth with primary cannabis and opioid dependence (the latter actually having comparable rates of cannabis use), and significantly more pronounced in the primary cannabis-dependent group. Without an assessment of working memory prior to substance exposure, the differential contributions of substance-induced vs. preexisting impairment are unclear. Lower scores in the cannabis group may reflect lower socioeconomic status (SES), which is typically correlated with cognitive performance. These findings highlight underrecognized cognitive impairment in youth with SUDs, especially inner-city cannabis-dependent youth. Modification of treatments to account for cognitive capacity and/or cognitive remediation interventions may be indicated to improve treatment outcomes.