Webster, MD, Lynn, et al. “A Double-Blind, Placebo-Controlled Study of Dual-Opioid Treatment With the Combination of Morphine Plus Oxycodone in Patients With Acute Postoperative Pain”. Journal of Opioid Management, vol. 6, no. 5, Jan. 2018, pp. 329-40, doi:10.5055/jom.2010.0030.