Cannabis use and duration of untreated psychosis: a systematic review and meta-analysis.

BACKGROUND: Duration of untreated psychosis (DUP) is an important predictor of outcome in first-episode psychosis (FEP). Cannabis use is highly prevalent in FEP patients and it is important to evaluate the potential impact of cannabis use on DUP. METHODS: A systematic review of the literature was conducted to identify articles reporting DUP in FEP cannabis users (CU+) and nonusers (CU-) respectively. Studies meeting inclusion criteria were entered into a meta-analysis. In addition, a comparative review was conducted of the relationship between substance use and DUP. RESULTS: Nine studies were identified reporting DUP in CU+ versus CU- patients. Of the pooled sample of 1726 FEP patients, 39% were cannabis users. Although in most studies DUP was shorter in cannabis using patients, meta-analysis did not detect a significant relationship between DUP and cannabis use. A trend towards shorter DUP in substance users was also apparent in the comparative review; although in none of the studies did this association reach statistical significance. DISCUSSION: This review and meta-analysis suggests a trend association between shorter DUP and cannabis use in FEP; especially when cannabis use is defined in terms of current or recent use (rather than lifetime use.) Further research should aim to clarify the relative effects of longstanding versus recent onset cannabis use on neurobiology, pathway to care and outcome in FEP.