Abstract
Recreational cannabis use has recently gained considerable interest as an environmental risk factor that triggers the onset of psychosis. To date, however, the evidence that cannabis is associated with negative outcomes in individuals at clinical high risk (CHR) for psychosis is inconsistent. The present study tracked cannabis usage over a 2-year period and examined its associations with clinical and neurocognitive outcomes, along with medication rates. CHR youth who continuously used cannabis had higher neurocognition and social functioning over time, and decreased medication usage, relative to non-users. Surprisingly, clinical symptoms improved over time despite the medication decreases.

Methods
The EDIPPP study was a national, multi-site clinical trial for preventing psychosis among young people, funded by the Robert Wood Johnson Foundation (2007–2011). This subsample included 210 CHR subjects assessed with the Structured Interview for Psychosis-Risk Syndromes (SIPS) (McGlashan et al., 2010). Written informed consent was obtained from participants≥18-years-old and parents of participants<18 (written assent from participant). The research protocol was approved by the IRB at each site.

Results
The overall CHR group consisted of mostly adolescents and young adults (Mean age=16.54, range 12–25). Gender–42.9% female; Race/Ethnicity–61.2% White, 8.2% African American, 5.9% Asian, 15.3% Hispanic). The average education level was 9.78 (SD=2.65), with 81.2% currently enrolled in school. At baseline, there was an overall significant difference between the subgroups on age, with the No Use subgroup being the youngest at 16.1-years-old and the other two subgroups about a year older on average…