OBJECTIVES: Patients with chronic pain frequently require strong opioids for pain relief. While most patients achieve adequate analgesia, a significant minority either suffers intolerable side effects and/or inadequate pain relief leading to opioid switching. The lack of a National Pain Care Registry does not permit a successful investigation in this topic. METHODS: Study population included all outpatients with chronic pain voluntarily participating in a cloud based medical surveillance system. Each patient was anonymously linked through an alphanumeric code to all opioid prescription (Anatomical Therapeutic Chemical code N02A) in a 18-month period. Chronic use was defined as taking the medication for more than 90 consecutive days. The prevalence of chronic use was calculated as the ratio between the number of subjects taking the medications more than 90 days consecutively and the total number of subjects with at least one opioid prescription. This study aims to assess (a) the pattern of opioid chronic use, (b) switching of active substance. RESULTS: Out of about 2,400 occasional users of opioids analgesics, 41 (1.7%) were chronic users. Women represented 70.7% of chronic users (N= 29). A total of 37 (90.2%) chronic users switched active substance at least once during the study period.  CONCLUSIONS: In this outpatient population, the majority of chronic users switched active substance at least once during the study period. These results may suggest that poor pain control or/and unintended side effects could be a leading cause of active substance switching. Otherwise, for patients with inadequate pain relief and intolerable opioid-related toxicity/adverse effects, a switch to an alternative opioid may be the only option for symptomatic relief. However, the evidence for the effectiveness of opioid switching does not appear to be established.