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Cannabis use by adolescents is a public health problem because it can cause cognitive impairment and educational deterioration. The objective of this study was to assess the prevalence and correlates of cognitive impairment among male adolescents with cannabis use in comparison with a control group. This is a case-control study that included 1682 adolescents who just finished their secondary school. A drug screen was made for all participants. Cognitive assessment using Montreal Cognitive Assessment (MoCA) scale was carried out for adolescents with positive urine screen for cannabis and a control group of adolescents with negative urine screen for drugs. The prevalence of cannabis use among adolescents was 2.14%. About one third of the cases started to use cannabis before the age of 15 years. Fiftysix percent used cannabis frequently ( > 4 times/wk). Adolescents with cannabis use were more likely to have cognitive impairment based on MoCA than controls (78% vs. 44%, P = 0.004). Cases were more likely to have impairment in naming, abstraction, orientation, and total MoCA score than controls. Adolescents who started cannabis use early (below 15 y) had impairment in visuospatial/executive, attention, language, abstraction, delayed recall, and total MoCA score compared with those who started late (above 15 y). In addition, adolescents who use cannabis frequently had impairment in all cognitive domains except naming compared with those who used it occasionally. To conclude, the current study found that adolescents with cannabis use were more likely to have cognitive impairment than controls and this impairment was associated with age of onset and frequency of cannabis use.

Purpose: Cannabis use among adolescents is a public health problem, one associated with intellectual and cognitive impairment. This study investigated the negative impact of cannabis use on adolescents’ school grades and intelligence. Methods: The study screened 1682 students during their university preadmission medical examination. Thirty-six students tested positive for cannabis, and 36 controls who tested negative for drugs were also included in the study. Sociodemographic and clinical data, school grades, and IQ (Wechsler Adult Intelligence Scale) scores were collected from cases and controls. Results: Cases were more likely to have lower final exam grades than controls in secondary and preparatory school, although they had higher grades than controls in primary school before starting cannabis use. Cases were more likely to have lower scores in verbal comprehension, perceptual reasoning, and total IQ than controls. However, the working memory and processing speed scores of both groups were equivalent. Students who started cannabis use at an earlier age (<15 y old) were more likely to have lower scores in total and all domains of IQ except verbal comprehension than students who started at a later age (>15 y old). There was an association between frequent use of cannabis and lower IQ scores (total and all domains). Conclusions: Cannabis use is associated with lower school grades and intelligence scores among adolescents, especially those who used cannabis frequently and at a young age.

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