Abstract
BackgroundAlthough studies have examined the association between tobacco and cannabis use in adolescence with subsequent cognitive functioning, study designs are usually not able to distinguish correlation from causation. MethodsSeparate patterns of tobacco and cannabis use were derived using longitudinal latent class analysis based on measures assessed on five occasions from age 13–18 in a large UK population cohort (Avon Longitudinal Study of Parents and Children). Cognitive functioning measures comprised of working memory, response inhibition, and emotion recognition assessed at 24 years of age. Mendelian randomization was used to examine the possible causal relationship between smoking initiation, lifetime cannabis use and cognitive functioning. ResultsWe found evidence of a relationship between tobacco and cannabis use and diminished cognitive functioning for each of the outcomes in the observational analyses. There was evidence to suggest that late-onset regular tobacco smokers (b=-0.29, 95 %CI=-0.45 to -0.13), early-onset regular tobacco smokers (b=-0.45, 95 %CI=-0.84 to -0.05), and early-onset regular cannabis users (b=-0.62, 95 %CI=-0.93 to -0.31) showed poorer working memory. Early-onset regular tobacco smokers (b = 0.18, 95 %CI = 0.07 to 0.28), and early-onset regular cannabis users (b = 0.30, 95 %CI = 0.08 to 0.52) displayed poorer ability to inhibit responses. Late-onset regular (b=-0.02, 95 %CI=-0.03 to - 0.00), and early-onset regular tobacco smokers (b=-0.04, 95 %CI=-0.08 to -0.01) showed poorer ability to recognise emotions. Mendelian randomization analyses were imprecise and did not provide additional support for the observational results. ConclusionThere was some evidence to suggest that adolescent tobacco and cannabis use were associated with deficits in working memory, response inhibition and emotion recognition. Better powered genetic studies are required to determine whether these associations are causal.
Highlights
Tobacco and cannabis use during adolescence, when the brain is still developing and undergoing considerable structural and function changes (De Bellis et al, 2000), is a major public health concern
There was evidence to suggest that late-onset regular tobacco smokers demonstrated poorer working memory performance (b=-0.29, 95 %CI=-0.45 to -0.13) and emotion recognition (b=-0.02, 95 %CI=0.03 to -0.00) compared to non-tobacco users
While early-onset regular tobacco smokers showed poorer performance across all three cognitive outcomes compared to the non-tobacco users: working memory (b=0.45, 95 %CI=-0.84 to -0.05), response inhibition (b = 0.18, 95 %CI = 0.07 to 0.28), and emotion recognition (b=-0.04, 95 %CI=-0.08 to -0.01)
Summary
Tobacco and cannabis use during adolescence, when the brain is still developing and undergoing considerable structural and function changes (De Bellis et al, 2000), is a major public health concern. The association between adolescent tobacco and cannabis use and subsequent cognitive functioning has received particular attention because certain cognitive functions (e.g. working memory, response inhibition, and emotion recognition) do not peak until early adulthood (Davidson et al, 2006; Thomas et al, 2007) in parallel with maturation of the prefrontal cortex (Sowell et al, 2001). Findings from two recent longitudinal studies of adolescents (Castellanos-Ryan et al, 2017; Morin et al, 2018) using a repeated measures design suggest that the association between cognitive functioning and cannabis use could be bidirectional. Results: We found evidence of a relationship between tobacco and cannabis use and diminished cognitive functioning for each of the outcomes in the observational analyses. Conclusion: There was some evidence to suggest that adolescent tobacco and cannabis use were associated with deficits in working memory, response inhibition and emotion recognition. Better powered genetic studies are required to determine whether these associations are causal
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