The Overdose Risk Behavior Questionnaire is a 9-item self-administered questionnaire. These questions measure the frequency, in the past 6 months, at which individuals used alone; used in a new place/environment; used other substances (alcohol, benzodiazepines, stimulants) within 2 hours of opioids; used more than one opioid; used more than the usual amount; and used inhaled or injected opioids. Response options were "never (0)," "rarely (1)," "sometimes (2)," "often (3)," and "very often (4)," except for #6, which was "never (0)," "once (1)," or "more than once (2)." The total risk score is an aggregation of responses to the individual questions. Sum score range: 0-32, higher scores indicate greater risk of overdose.