“…The study designs included 6 randomized controlled trials (RCTs), 18,20,22,26,30,33 1 prospective cohort, 19 12 retrospective cohort, 21,[23][24][25]29,35,[37][38][39][40]43,44 2 case-cohort, 27,40 5 case-control, 17,32,34,36,42 and 3 cross-sectional studies (2 combined with retrospective cohorts) 23,31,32 (Table 1). Most studies were conducted among chronic noncancer pain patients (n = 15) 19-26,30,33,35,39,40,43,44 ; however, some studies were conducted among all opioid users including cancer and acute pain patients ( Table 1).…”