Study design and procedure
This Phase II study used a randomized, double-blind, placebo-controlled, within-subject study design. Potential participants completed a phone and in-person screening, during which they provided a urine sample that was tested for recent drug exposure and pregnancy (for premenopausal females) and were excluded if they reported past month opioid exposure. Eligibility was determined based on medical history and physical including ECG, hepatic, hematologic, and chemistry functioning (see Online Supplement Table 