The VASC will be administered to assess potential variations in the subjective craving effects associated with heroin. Following the administration of the investigational drug, craving induced in response to the cue sessions in the clinic will be measured. Note, cue sessions occur consecutively in the same test day. In this way, changes in craving from baseline (pre-cue to post-cue within each test day), as well as changes in cue-induced craving over the short-term (test day 1 through test day 4 a week later) will be monitored and measured. VASC scale ranges from 0 for "Not Craving at All" to 10 for "Extremely Craving."

Subjects will be asked to complete the short version of the HCQ on their own time at home and bring it with them when they return for their next visit. Upon arrival to the clinic, subjects will also complete an HCQ with the coordinator to assess daily baseline cravings. This questionnaire will help us assess changes in craving generated outside of the clinical laboratory session from test day 1 through test day 4 (1 week later). Each item is scored on a scale ranging from 1 for "Strongly Disagree" to 7 for "Strongly Agree." Sum of all 14 items are scored and added. Mean scores reported below. Total Score Range: 14 (less cravings) - 98 (more cravings).