Chronic opioid exposure has been linked with neurocognitive impairments. Evidence of residual impairment with cannabis use is less consistent. We investigated whether patients with opioid and cannabis dependence perform poorly compared with those with opioid dependence alone.We recruited three groups of participants aged 18 to 55 years: opioid and cannabis dependence (OCaD; n = 21), only opioid dependence (OD; n = 19), and a control group (HC; n = 20). Subjects with other substance use, human immunodeficiency virus, head injury, epilepsy, and severe mental illness were excluded. Cognitive tests, performed after at least 1 week of abstinence, consisted of the Wisconsin card sorting test (WCST), Iowa gambling task (IGT), trail making tests A and B (TMT-A and B), verbal and visual N-back test (NBT), and standard progressive matrices for intelligence quotient (IQ). The general linear model was used to compare the groups with age and years of education as covariates.IQ and severity of opioid dependence were comparable in the three groups. The mean duration of cannabis use was 76.2 (±39.4) months. Compared with the HC, both OD and OCaD had significant impairment on the IGT, WCST, TMTs, and NBT. No significant group difference was observed between the OD and OCaD groups.Opioid dependence is associated with impairments in decision making, executive function, working memory, and attention. Co-morbid cannabis dependence had similar profiles of cognitive impairments.Co-morbid cannabis dependence might not add on to the existing cognitive dysfunction in opioid dependence. Further studies should be done with a larger sample. (Am J Addict 2020;00:00-00).
