Chronic use effects, or just the effects of using chronic? Examining the roles of lifetime and current severity of cannabis use in neurocognitive performance and ADHD symptoms.

Abstract

Cannabis use is becoming increasingly prevalent in Canada and the United States, where legality and public perception have recently shifted to be more permissive of recreational use. Despite established negative health consequences associated with persistent use, there remains considerable debate in the scientific community surrounding the potentially harmful effects of cannabis use on human cognition. Evidence exists that heavy cannabis use predicts diminished performance within several neurocognitive domains and also predicts greater risk of having ADHD. Further evidence suggests that earlier age of first cannabis use strengthens these associations, however the findings in these literatures are mixed and in need of further delineation. This thesis sought to examine continuous associations among current cannabis use severity, age of first use, neuropsychological performance, and ADHD symptomatology. Two studies using large samples of community adults were conducted. Study 1 analyzed data from the Human Connectome Project, and examined performance on a battery of neuropsychological measures among young adults, and found recent use to be the strongest predictor of differences in episodic memory and processing speed, and CUD predicted lower fluid intelligence. Lifetime exposure to cannabis was not associated with any outcome measures. Study 2 examined similar associations in a sample of adults representative of the Hamilton community, and also included self-reported symptoms of ADHD. Study 2 found current cannabis use severity to be predictive of more impulsive reward preferences, and also of both hyperactive-impulsive and inattentive symptoms of ADHD. Both studies found a lack of support for the role of age of first cannabis use in differential cognitive performance, and also failed to find associations between cannabis involvement and several cognitive domains such as working memory, behavioural inhibition, executive function, and psychomotor dexterity. These findings challenge some of the current literature, and highlight the necessity of further investigation to better understand interrelationships among cannabis use, cognition, and ADHD.