1.4　Side Effects to Treatment

While strong opioids are effective to relieve pain in CP patients，opioids frequently result in gastrointestinal side effects，including constipation，reflux，nausea and abdominal pain（Brock et al.2012）.Chronic abdominal pain was reported to be 58%in patients treated with opioids for non-cancerous diseases（Tuteja et al.2010）.Other medications that affect bowel motility and disturbed GI motor function due to exocrine pancreatic insufficiency may also indirectly contribute to the bacterial overgrowth that is reported in up to 40%of the patients and may result in abdominal distension and pain（Layer 1995；Casellas et al.1998）.(https://www.daowen.com)

Complications to surgical and endoscopic therapy can also result in abdominal pain.However，no studies have examined the relative contribution to abdominal pain due to surgical complications in CP.