The combined use of marijuana and tobacco is associated with both structural changes to the brain and cognitive effects, according to new data published in Behavioural Brain Research.
Francesca M. Filbey, of the University of Texas, and colleagues examined the effects of tobacco, marijuana, and their combined use on the brain and behavioral relationships. Participants included marijuana-only users (n=36), nicotine-only (n=19), combined marijuana and nicotine users (n=19), and non-using health controls (n=16). Total bilateral hippocampal volumes and memory performance (WMS-III logical memory) were compared across groups controlling for total brain size and recent alcohol use.
The researchers found that the marijuana and marijuana+nicotine groups had smaller total hippocampal volumes compared to nicotine-only and control groups. No significant difference was observed between groups for immediate and delayed story recall. Controls showed a trend towards larger hippocampal volumes being associated with better memory scores, and interestingly, the marijuana+nicotine group showed an inversion where smaller hippocampal volume was associated with better memory.
The results do suggest that there are abnormalities between brain and behavior relationships, especially those underlying memory processes, in people who use both marijuana and tobacco, however further research needs to be conducted in order to fully understand the complex relationship.
Combined use of marijuana (MJ) and tobacco is highly prevalent in today’s population. Individual use of either substance is linked to structural brain changes and altered cognitive function, especially with consistent reports of hippocampal volume deficits and poorer memory performance.
However, the combined effects of MJ and tobacco on hippocampal structure and on learning and memory processes remain unknown. In this study, we examined both the individual and combined effects of MJ and tobacco on hippocampal volumes and memory performance in four groups of adults taken from two larger studies.