Structural MRI Findings in Long-Term Cannabis Users: What Do We Know?

Abstract

In animal studies, tetrahydrocannabinol (THC) has been found to affect brain morphology, particularly within areas rich in cannabinoid receptors (e.g., hippocampus, cerebral cortex). While cannabis remains the most widely used illicit drug worldwide, there has been limited work investigating its effects on human brain tissue. In this paper, we conducted a systematic review of existing structural magnetic resonance imaging studies to examine whether cannabis use is associated with significant changes in brain anatomy. We identified only 13 structural neuroimaging studies, which were diverse in terms of sample characteristics (e.g., age of participants, duration and frequency of use) and methodology (e.g., image analysis). No study found global structural changes in cannabis users, although six studies reported regional alterations. While changes in the hippocampus and parahippocampus were frequently identified, the findings were inconsistent across studies. The available literature also provides some evidence that regional structural changes are associated with cannabis use patterns (particularly cumulative dosage and frequency of use), as well as measures of psychopathology (e.g., measures of depressive and psychotic symptoms). Together, these structural imaging findings suggest that THC exposure does affect brain morphology, especially in medial–temporal regions. Given the small literature available and the limitations of studies to date, further research is clearly required, particularly given the prevalence of cannabis use worldwide.

Keywords :

• Cannabis
• brain
• morphology
• hippocampus
• parahippocampus
• amygdala

THE AUTHORS

Valentina Lorenzetti is currently undergoing her PhD at the Melbourne Neuropsychiatry Centre, Department of Psychiatry, the University of Melbourne. Her current PhD work utilizes neuroimaging techniques to investigate the neural correlates of heavy cannabis use and comorbid mental health problems. She is also involved in projects investigating the neural underpinnings of emotion and its anomalies in a range of mental disorders including depression. Finally, she has an interest in the concurrent applications of functional MRI and psychophysiological techniques to understand emotion processing in neuropsychiatric populations. Her long-term career aspirations are to continue investigating brain–behavior relationships associated with affective dysregulation in substance (ab)use and psychiatri

Dan Lubman, MB ChB, PhD, FRANZCP, FAChAM, is currently appointed as an Associate Professor at the Orygen Youth Health Research Centre, the University of Melbourne. He heads a clinical research unit that investigates problematic substance use and co-occurring mental health issues in young people. This includes a number of pharmacological and psychological treatment trials in psychosis and depression, as well as neuropsychological and neuroimaging studies examining the neurobiology of addiction.

Sarah Lauren Whittle, PhD, is a Post Doctoral Research Fellow at Orygen Youth Health Research Centre and the Melbourne Neuropsychiatry Centre, the University of Melbourne. Her area of research interest focuses on understanding the neurobiological underpinnings of common psychiatric disorders and risk factors. Dr. Whittle has particular expertise in structural neuroimaging analysis in varying populations.

Nadia Solowij, PhD, is a Senior Lecturer and Researcher in the School of Psychology, University of Wollongong. Nadia spent 15 years at the National Drug and Alcohol Research Centre, University of New South Wales, Sydney, establishing her primary area of expertise on the long-term cognitive effects of cannabis. She has used psychophysiological, neuropsychological, and brain imaging techniques in her investigations and has over 70 scientific publications including her book Cannabis and cognitive functioning (Cambridge University Press). Her current research focuses on brain structure and memory function in adult and adolescent cannabis users and people with schizophrenia and comorbid cannabis use.

Murat Yücel, Clinical PhD (Neuropsychology) MAPS, is currently appointed as an Associate Professor in the Department of Psychiatry, the University of Melbourne. He currently heads the Impulsive and Compulsive Behaviour Group at the Melbourne Neuropsychiatry Centre, and is a Research Leader in Neuroimaging at ORYGEN Youth Health Research Centre.