Daily cannabis users are more likely to meet the criteria for an ADHD diagnosis, including hyperactive-impulsive symptoms (Loflin et al, 2014), which may indicate a relationship between cannabis use and these ADHD symptoms. There is also an interest in what age an individual first uses cannabis and if earlier cannabis use results in more severe ADHD symptoms and neurocognitive deficits. This study assessed the following in a relatively large sample of adults: (a) how cannabis use affected specific neurocognitive tasks; (b) associations between cannabis use with hyperactive-impulsive and inattentive symptoms of ADHD; and (c) the relationship between the severity of cannabis use and age of first cannabis use.
Eligibility criteria for this study were: aged 18‒65 years; willingness to participate in future mental health and addiction studies; sufficiently literate; able to complete online assessments; and no medical condition that would preclude participation in future studies. Only participants who reported any lifetime use of cannabis were included in this analysis. Participants completed online assessments, providing information on cannabis use, other substance use, ADHD symptoms and neurocognitive assessments. These included measurements of attention and working memory, impulsiveness, intelligence and risk-taking. Dimensional relationships were investigated using multiple hierarchical regressions.
A total of 1008 adults were included in the study, 56% of whom were female, with a mean (standard deviation) age of 38.49 (13.25) years. Using a covariate model (covariates: age, gender, income, alcohol use and tobacco use), higher cannabis use was significantly associated with increased hyperactive-impulsive and inattentive ADHD symptoms (p < 0.01) but not with any of the other cognitive measures. An exploratory subgroup analysis of young adults (n = 371; aged 18‒30 years) found that greater cannabis use was associated with digit span forward (a measure of attention and working memory; p = 0.046) and hyperactive ADHD symptoms (p = 0.006), and was associated with greater delay discounting (a measure of impulsivity; p = 0.001), hyperactive (p = 0.026) and impulsive (p = 0.19) ADHD symptoms in high-risk cannabis users (n = 161). Age of first cannabis use was not significantly associated with any neurocognitive variables or hyperactive (p = 0.587) or inattentive (p = 0.267) symptoms of ADHD in any of the analyses.
These data should be interpreted in light of several considerations. For example, these analyses did not take into account any history of conduct disorders. It is possible that after taking into account behavioural problems in adolescence, any associations between cannabis use and the symptoms of ADHD would be reduced. Additionally, this study used an assessment of cannabis use that is relatively coarse, a more refined assessment would include information about the strength of ∆9-tetrahydrocannabinol (THC), types of products used, the method of administration and patterns of use, as well as biochemical markers for recent THC exposure and cumulative used.
The authors concluded that these findings “provide evidence of a link between current cannabis misuse and both hyperactive and inattentive ADHD symptoms”. There were no associations between cannabis use and verbal intelligence, attention, working memory, propensity for risk or behavioural inhibition. There was also no evidence associating early initiation of cannabis with reduced cognitive performance or ADHD symptoms.
Loflin M, Earleywine M, De Leo, J et al. Subtypes of attention deficit-hyperactivity disorder (ADHD) and cannabis use. Subst Use Misuse 2014; 49: 427-434.
Petker T, DeJesus J, Lee A, et al. Cannabis use, cognitive performance, and symptoms of attention deficit/hyperactivity disorder in community adults. Exp Clin Psychopharmacol 2020; Epub ahead of print.