1. Owen GT, Burton AW, Schade CM, Passik S (2012) Urine drug testing: current recommendations and best practices. Pain Physician 15:ES119–ES133
2. Centers For Disease Control And Prevention Public Health Service U S Department Of Health And Human Services (2016) Centers for disease control guideline for prescribing opioids for chronic pain—United States.
http://www.cdc.gov/mmwr/volumes/65/rr/pdfs/rr6501e1.pdf
. Accessed 15 Jun 2017
3. Gutstein HB, Akil H (2006) Opioid analgesics. In: Brunton LL, Lazo JS, Parker KL (eds) The pharmacological basis of therapeutics, 11th edn. McGraw-Hill Companies Inc., Goodman & Gilman’s
http://www.accessmedicine.com/content.aspx?aID=940653