Immediately prior to and at specified time points after administration of a single dose of study drug, subjects will complete the following subjective scales: visual analog scales (VAS) for any drug effect, high, good effects, bad effects, liking, and sick; and adjective ratings (agonist and antagonist scales). Subjects will also be asked to complete a money versus drug questionnaire at various time points after drug administration. Observers will complete an adjective rating scale. Safety will be monitored by vital signs (heart rate, blood pressure, respiratory rate, and pulse oximetry), adverse events assessments, clinical laboratory tests, physical examinations and electrocardiograms (ECGs). In addition, pupil diameter (measured by photographs) will be obtained to monitor for physiological signs of opioid effects.