Thirty-two participants at clinical high risk (CHR) for psychosis were randomized to receive either cannabidiol (CBD) 600 mg/day (CHR-CBD) or placebo (CHR-P) for one week. The CHR participants and 25 healthy controls (HC) then performed a psychosocial stress task. The primary outcome was the neuroendocrine response to stress measured by serum cortisol levels. Other outcomes of interest included subjective measures of anxiety and stress associated with public speaking. Between the HC, CHR-CBD, and CHR-P groups, in order, a significant linear decrease in cortisol levels was observed alongside significant linear increases in both anxiety and stress, suggesting beneficial effects of CBD treatment.