Impact of cannabis use on thalamic volume in people at familial high risk of schizophrenia

Background No longitudinal study has yet examined the association between substance use and brain volume changes in a population at high risk of schizophrenia. Aims To examine the effects of cannabis on longitudinal thalamus and amygdala-hippocampal complex volumes within a population at high risk of schizophrenia. Method Magnetic resonance imaging scans were obtained from individuals at high genetic risk of schizophrenia at the point of entry to the Edinburgh High-Risk Study (EHRS) and approximately 2 years later. Differential thalamic and amygdala-hippocampal complex volume change in high-risk individuals exposed (n = 25) and not exposed (n = 32) to cannabis in the intervening period was investigated using repeated-measures analysis of variance. Results Cannabis exposure was associated with bilateral thalamic volume loss. This effect was significant on the left (F=4.47, P=0.04) and highly significant on the right (F=7.66, P=0.008). These results remained significant when individuals using other illicit drugs were removed from the analysis. Conclusions These are the first longitudinal data to demonstrate an association between thalamic volume loss and exposure to cannabis in currently unaffected people at familial high risk of developing schizophrenia. This observation may be important in understanding the link between cannabis exposure and the subsequent development of schizophrenia.