Boulanger L, Wu N, Chen SY, Nagar S, Fraser K, Bernauer MJ, Zhao Z, Zhao Y. Predictors of pain medication selection among patients diagnosed with fibromyalgia. Pain Pract. 2012 Apr;12(4):266-75.
Candrilli SD, Davis KL, Iyer S. Impact of constipation on opioid use patterns, health care resource utilization, and costs in cancer patients on opioid therapy. J Pain Palliat Care Pharmacother. 2009 Sep 1;23(3):231-41.