Behavioral Effects of Drugs Inpatient 44 Neurobehavioral Mechanisms of Opioid Choice

Inclusion Criteria: * Individuals must meet criteria for moderate/severe opioid use disorder, report past month opioid misuse, and be physically dependent on short-acting opioids (e.g., heroin, hydromorphone, fentanyl), as evidenced by either urine sample positive for recent opioid use during each visit or if opioid negative, displaying frank withdrawal during screening. * History of intravenous opioid use. * Baseline O2 saturation of 95% or greater. * Between the ages of 18-50 years. * Female subjects must be using an effective form of birth control (e.g., birth control pills, surgical sterilization, IUD, cervical cap with a spermicide, or abstinence). Urine pregnancy tests will be conducted prior to sessions to ensure that female subjects do not participate if pregnant. * Able to speak and read English. * Otherwise healthy. Exclusion Criteria: * History of, or current, clinically significant physical disease (e.g., respiratory disease \[asthma, COPD, sleep apnea\], impaired cardiovascular functioning, seizure disorder or CNS tumors) or current or past history of psychiatric disorder that would limit compliance in the studies, other than substance use disorder. * Meet diagnostic criteria for psychoactive substance use disorder for substances other than opioids (OUD subjects only) or nicotine/caffeine that would require detoxification (i.e., alcohol, benzodiazepines or barbiturates). Negative urine/breath samples for these substances, and the absence of withdrawal, will be required during screening. * Contraindications for MRI scanning (e.g., pacemaker, metal implants, claustrophobia, or any other implanted medical device). * Vision or hearing problems that would preclude completion of experimental tasks. * Poor venous access. * Regular use of other medications, with the exception of hormone-based contraceptives for female subjects, daily multivitamins or short-term antibiotic prescriptions. * At risk for respiratory complications and have predictors of difficult bag mask ventilation (e.g., dentures, very full beard), in case emergency respiratory intervention is needed. * Seeking treatment for SUD or currently taking buprenorphine or methadone as the primary opioid of use.