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.

An MRI study of white matter tract integrity in regular cannabis users: effects of cannabis use and age

“…Moreover, exogenous cannabis use has been shown to interfere with normal pruning processes (Rubino et al 2015), thus possibly elevating measures of white matter connectivity. Alternatively, these increases in white matter may arise as a reactive response to reduced gray matter (Yücel et al 2008;Lorenzetti et al 2010) or be an imaging artefact due to smaller axons leading to falsely elevated axon density (Beaulieu 2002). Additionally, differentially altered white matter integrity across age groups, which to our knowledge has not been previously examined, may explain the seemingly disparate reports of both increases (DeLisi et al 2006;Jacobus et al 2009;Bava et al 2010;Filbey et al 2014) and decreases (Gruber and Yurgelun-Todd 2005;Arnone et al 2008;Ashtari et al 2009;Gruber et al 2011;Gruber et al 2014) in white matter integrity in cannabis users.…”

Alteration to hippocampal shape in cannabis users with and without schizophrenia

“…There is growing evidence that long-term or heavy cannabis use impacts upon brain structure and function, particularly in regions known to be affected in schizophrenia, such as the hippocampus (Ashtari et al, 2011;Lorenzetti et al, 2010;Solowij and Michie, 2007;Solowij et al, 2012). We have previously reported doserelated reductions in hippocampal volume in otherwise healthy chronic cannabis users that were associated with subclinical positive psychotic symptoms (Yücel et al, 2008), and were of a magnitude similar to that observed in schizophrenia (e.g.…”

Brain volume in male patients with recent onset schizophrenia with and without cannabis use disorders

“…This finding was corroborated by Battistella and col leagues, 28 who reported an effect of dosage as well, since regu lar cannabis users had decreased grey matter volumes in the temporal pole and parahippocampal gyrus compared with oc casional users. Lorenzetti and colleagues 29,30 described in their reviews a trend for decreases in brain volumes in samples with high but not lowfrequency cannabis use, all of which sug gests an adverse effect of cannabis.…”