Date of Award

Spring 1-1-2018

Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Kent E. Hutchison

Second Advisor

Angela D. Bryan

Third Advisor

Mark A. Whisman

Fourth Advisor

Scott Vrieze

Fifth Advisor

Ryan K. Bachtell


Scientific literature delineating potential negative impacts or neuroprotective benefits of marijuana consumption has not kept pace with societal changes in acceptance of its recreational use. Further exploration of marijuana use among older adults may help clarify global risks or neuroprotective benefits of using marijuana. This study collected structural MRI and cognitive assessments within a sample of recreational marijuana users age 60 years and older and healthy control non-users in order to report basic associations between marijuana use and brain structure, and, importantly, associations between brain structure and cognitive function.

Marijuana users (n=28) and controls (n=28) were not different in terms of global brain structural measures, but groups showed diffuse areas of difference throughout the brain. Users (n=28) showed slightly poorer working memory than controls (n=10). Lifetime users (n=15) performed poorly compared to both short-term users (n=13) and controls (n=10) in executive function, and poorly compared to controls in general cognition. Estimated total THC consumption in the last 90 days showed negative association with total gray matter volume and diffuse clusters in whole-brain models, and years of regular marijuana use showed consistent negative associations with cognitive performance in executive function, processing speed, and total cognition.

The current study is an important contribution to the field in terms of addressing several of the common limitations of existing research and providing innovation in exploring marijuana use in a novel and growing population. Study results suggest that lifetime marijuana use at a recreational level does not have a strong and consistent effect on brain structure in comparison to substances like alcohol, but it does appear to have a negative association with aspects of cognitive functioning. From a harm reduction perspective, it is valuable to note that any cognitive harms associated with long-term marijuana use may be reduced by consuming strains with lower THC concentrations with less frequency.