Despite the high prevalence of cannabis use in schizophrenia, few studies have examined the potential relationship between cannabis exposure and brain structural abnormalities in schizophrenia.

To investigate prefrontal grey and white matter regions in patients experiencing a first episode of schizophrenia with an additional diagnosis of cannabis use or dependence (n=20) compared with similar patients with no cannabis use (n=31) and healthy volunteers (n=56).

Volumes of the superior frontal gyrus, anterior cingulate gyrus and orbital frontal lobe were outlined manually from contiguous magnetic resonance images and automatically segmented into grey and white matter.

Patients who used cannabis had less anterior cingulate grey matter compared with both patients who did not use cannabis and healthy volunteers.

A defect in the anterior cingulate is associated with a history of cannabis use among patients experiencing a first episode of schizophrenia and could have a role in poor decision-making and in choosing more risky outcomes.