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2. Urine drug testing in chronic pain;Christo;Pain Phys,2011
3. Opioid prescriptions by U.S. primary care physicians from 1992 to 2001;Olsen;J Pain,2006
4. Trends and geographic variation of opiate medication use in state Medicaid fee-for-service programs, 1996 to 2002;Zerzan;Med Care,2006
5. IMS Health. National Prescription Audit. 2013. (Accessed July 8, 2016, at http://www.imshealth.com/files/web/Corporate/News/Top-Line Market Data/US_Top_25_Medicines_Dispensed_Prescriptions.pdf.)