Introduction: Research evaluating the neuropsychological effects of cannabis has yielded mixed findings, with some studies finding cognitive deficits in cannabis users (primarily in learning and memory) and others finding no significant effects. It is important to understand how clinicians perceive this discrepancy in the empirical literature. However, no studies have assessed neuropsychologists' beliefs regarding the effects of cannabis on cognitive functioning. Thus, this study sought to evaluate how patient and cannabis-use factors influence neuropsychologists' perceptions of cannabis's cognitive effects. Method: Neuropsychologists (N = 261) read eight vignettes, each depicting cannabis users varying in age, gender, and cannabis-use history (frequency, duration, and recreational/medicinal use). Respondents rated the anticipated effects of cannabis in each vignette on nine cognitive domains. Mixed effects linear regression modeled the ratings of cognitive abilities as a function of neuropsychologist, neuropsychologists' training, vignette, patient age, gender, and frequency/duration/type of cannabis use, and treated neuropsychologist and vignette as random effects. Results: Duration of use had the most notable effect on neuropsychologists' ratings, with a small (0.1 to 0.2 SDs) yet statistically significant (p .001) negative effect on each cognitive domain. Male gender and medicinal use also predicted lower cognitive ratings. Differences in ratings between neuropsychologists accounted for 73 of the total variability in each domain, whereas variability due to vignette alone was negligible (1). Conclusions: Results suggest that neuropsychologists believe that cannabis use results in broad but mild cognitive deficits, consistent with meta-analytic findings of active chronic cannabis users, particularly for males and for individuals using cannabis for medicinal purposes. Interestingly, neuropsychologists expected fewer cognitive effects in recreational cannabis users. Further, duration of use (rather than frequency) was believed to be the primary factor contributing to cognitive deficits.
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