Das, MBBS, MD, M.; Jain, MSc, PhD, CChem FRSC (UK), R.; Dhawan, MBBS, MD, A.; Kaur, MBBS, MD, A. Assessment of Abuse Liability of Tramadol Among Experienced Drug Users: Double-Blind Crossover Randomized Controlled Trial. J of Opioid Management 2016, 12, 421-430.