Background: 75-80% of pts with advanced cancer report pain and almost all receive opioids. There is limited knowledge on deviations from prescribed opioids (MD-Rx) and barriers to pain control. Poor adherence to opioids has been reported in 49-70% of pts. Methods: In this prospective study, we examined the frequency and predictors of pt-reported opioid deviation, and barriers to opioid use in 198 outpatients followed at the Supportive Care Clinic (SCC). We collected pain score (0-10), MD-Rx, confidential patient-reported prescription (Pt-Rx) and opioid intake (Pt-In), barriers to pain management (Barriers Questionnaire II, BQ-II), and adherence to medications (modified Morisky scale, MMS). We defined opioid deviation as <70% or >130% from prescribed dose. Results: Median age was 55, 91 (46%) females, 187 (94%) had solid tumors. The median pain was 4 (IQR 3-7). The median morphine equivalent daily dose was 120mg [Q1-Q3 45-270] for MD-Rx, 100mg [40-270] for Pt-Rx, and 100mg [30-250] for Pt-In. There was a high correlation between MD-Rx and Pt-Rx for regular [r = 0.9, p<0.001], and regular + breakthrough opioids intake [r = 0.94, p<0.001]. 19/198 pts (9.6%) deviated: 11 (6%) used lower doses than prescribed, and 8 (4%) used higher doses. Deviation was more frequent in males [p=0.04] and non-whites [p=0.027]. Non-white race was also associated with higher barriers to opioid use (mean BQ-II 2.16 for other races and 1.76 for African-Americans vs. 1.6 for whites, p=0.01). Higher barrier by BQ-II was in turn associated with lower adherence according to MMS (mean BQ-II 2.0 vs. 1.6, p=0.007 in the motivation domain; mean BQ-II 2.13 vs. 1.57, p=0.0001 in the knowledge domain). Higher BQ-II scores were also associated with taking less/no opioids due to cost (p=0.0017). Conclusions: A small percentage of interdisciplinary supportive care pts reported confidential opioid deviation and most commonly towards less dose intake. These findings suggest SCCs are more successful than other settings in opioid management. Non-white race and male gender were associated with higher risk of opioid deviation. Non-white race was also associated with higher barrier to opioid use.