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Langley-DeGroot M, Ma JD, Hirst J, Roeland EJ.Langley-DeGroot M, et al.J Pain Palliat Care Pharmacother. 2015 Jun;29(2):148-52. doi: 10.3109/15360288.2015.1035831.J Pain Palliat Care Pharmacother. 2015.PMID: 26095486Review.