Neurological Soft Signs in Patients with Psychosis and Cannabis Abuse: A Systematic Review and Meta-Analysis of Paradox

Background: Although neurological soft signs (NSSs) have been consistently associated with schizophrenia and a variety of risk factors, few studies have focused on the association between NSSs and environmental factors such as cannabis use, particularly in patients with first episode psychosis (FEP). Aims: To review studies that have specifically investigated the association between NSSs and cannabis use in subjects who suffer from psychosis, and more specifically in FEP. Methods: A review of studies investigating the associations between neurological function in psychotic patients and cannabis use. Results: A total of 5 studies met our inclusion criteria. Two of these included data only from patients with FEP. Four studies concluded that patients with psychosis and particularly FEP who consumed cannabis showed fewer NSSs. Conclusions: Four possible explanations are suggested for the paradoxical relationship between cannabis use and NSSs in FEP. First, heavy cannabis users present with different acute responses to cannabis use than do occasional cannabis users. Second, the psychoses developed by patients who consume cannabis follow different physio-pathological pathways that include fewer neurodevelopmental abnormalities. Third, the direct effect of cannabis on the Central Nervous System (CNS) may be responsible for the paradox. Finally,severe NSSsare associated with other clinical characteristics that would limit a subject's personal access to cannabis.