Opioid-induced constipation (OIC) can limit the clinical benefit of opioid treatment. This post-hoc analysis evaluated the association between the Rome IV diagnostic criteria and other measures for OIC, including the Bowel Function Index (BFI), correlation between demographics and OIC onset, impact of OIC on pain treatment, and impact of patient–healthcare professional (HCP) communication on patient satisfaction. Patients recorded bowel habits in paper diaries for 14 days following opioid initiation. Study-specific questionnaires were used to evaluate patient awareness of OIC and satisfaction. Patients were ≥20 years old, initiating strong opioid therapy for cancer pain, had an ECOG PS ≤ 2, and had no constipation (≥3 bowel movements within 7 days of enrollment). A total of 220 patients were enrolled. The sensitivity and specificity of BFI for identifying OIC were 81.2% and 54.7%, respectively. Age <65 versus ≥65 years (odds ratio (OR) = 0.510, 95% confidence interval (CI): 0.267–0.977) and the presence or absence of comorbidities (OR = 0.443, 95% CI: 0.221–0.885) were correlated with OIC onset. The proportion of inpatients with sustainable pain control at week 2 was similar in patients with or without OIC (60.0% vs. 67.2%, respectively). By patient assessment, there was a significant correlation between an adequate level of patient–HCP communication and satisfaction with OIC treatment (OR = 9.538 (95% CI: 1.577–57.681)). Using BFI to screen for OIC represents a valid approach in patients with cancer pain. Patient–HCP communication is essential for effective management of OIC in patients with cancer pain.