REEFER MADNESS: ADOLESCENT CANNABIS USE AND COGNITION. Megan
Ann Harvey. A thesis submitted for the degree of Doctor of Philosophy.
REEFER MADNESS: ADOLESCENT CANNABIS USE AND COGNITION
Megan Ann Harvey A thesis submitted for the degree of Doctor of Philosophy At the Christchurch School of Medicine & Health Sciences University of Otago Dunedin New Zealand December 2006
Abstract
Introduction Research indicates cannabis continues to be the most commonly used illicit drug in Western countries. Furthermore, adolescent rates of use are high. The physiological effects of cannabis are well researched and the understanding of the mental health effects is advancing. The effects on cognitive functioning from cannabis are less consistently demonstrated. The non-acute effect of cannabis use on adult cognition has been relatively extensively researched. However, there has been much less examination of adolescent cognition.
Aims The present study investigated the non-acute relationship between cannabis and cognitive function in a sample of adolescents with a continuum of cannabis use. It aimed to answer the questions: Is there a significant relationship between non-acute cannabis use and cognitive function in adolescents aged 13 to 18 years; and if there is a significant relationship, are there additional predictor variables that can account for the relationship beyond the use of cannabis?
Method Seventy adolescents were recruited from clinical and community sources, and through newspaper advertisements. They completed a baseline and three-month follow-up interview. Each time, after 12 hours self-reported abstinence from cannabis, adolescents completed a two-hour interview covering: demographics; drug use; cognitive performance; and psychiatric and general functioning. Current and lifetime drug use was assessed with an alcohol and drug use history, and the Timeline Follow-Back questionnaire. Cognitive assessment incorporated computerised tasks with the Cambridge Neuropsychological Test Automated Battery (including Motor Skills, Rapid Visual Information Processing, Spatial Working Memory, Intra/Extra-Dimensional Shift, Paired Associated Learning and Spatial Span tasks) and the pen and paper tests of the Rey Auditory-Verbal Learning Test, Digit Span, and Symbol Digit Modalities Test. Premorbid intelligence was assessed with the Wechsler Abbreviated Scale of Intelligence. Psychiatric functioning was assessed with the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders Fourth Edition as well as measures of Attention Deficit Hyperactivity Disorder and Conduct Disorder and the additional measures of depression on a Visual Analogue Scale of current mood, the Beck Depression Inventory and the Hamilton Depression Rating Scale. General functioning was measured through the General Assessment of Functioning scale.
Results At baseline adolescents who were regular cannabis users (more than once a week) had a significantly poorer performance on four measures of cognitive function reflecting attention, spatial working memory and recall. Cannabis use remained an independent predictor of performance on the spatial working memory and verbal recall measures after additional predictor variables were included in a multivariate regression analysis. Of the 70 adolescents interviewed at baseline, 47 (67%) were followed-up. At follow-up only one measure of cognitive performance, assessing spatial working memory, was significantly related to cannabis use. This relationship again remained significant after additional predictor variables were accounted for in regression.
Conclusions The results suggest that aspects of adolescent cognitive function, particularly working memory, are independently related to the frequency of cannabis use beyond acute intoxication. These results are consistent with findings in both the adult and, limited, adolescent literature on non-acute cannabis use and cognition. The findings have implications for adolescent education and drug use treatment.
