Incidence of opioid-induced constipation in non-cancer patients using weak opioids for chronic pain in Japan: a cohort study.

Opioid-induced constipation (OIC) is a common adverse drug reaction of opioids. However, limited evidence exists regarding the incidence of OIC, as diagnosed using the Rome IV criteria, in non-cancer patients newly prescribed weak opioids for chronic pain in Japan. This study aimed to clarify the incidence of OIC in patients aged ≥ 18 years who were newly prescribed weak opioids in outpatient settings in Japan. This study was conducted from February 1, 2023, to July 13, 2024 (trial registration number: UMIN000050203), using a patient-reported, web-based questionnaire survey. Of the 64 participants (mean age: 53.2 years) included, 63 participants received weak opioids for ≥ 7 days. The cumulative incidence of OIC (95% confidence interval) was 30.2% (20.4-43.1) in the first week and increased to 49.2% (37.7-62.1) by the end of the second week. Common symptoms included straining (66.7%), incomplete evacuation (49.2%), and hard stools (22.2%). Although the results were derived from exploratory analyses, no risk factors for the development of OIC were identified among participants' demographics, clinical characteristics (including pain sites), or the weak opioid usage and dosage. These findings emphasize the need for caution regarding the onset of OIC when initiating pain management with weak opioids.