Introduction Opioid-induced constipation (OIC) is the most common side effect of opioids. Weak opioids are often prescribed for non-cancer chronic pain in Japan; however, data on laxative use are scarce. We evaluated the real-world prescription patterns of laxatives for OIC in patients administered weak opioids for non-cancer pain in Japan. Methods In this retrospective cohort study, we extracted data from a Japanese health insurance claims database for patients with chronic non-cancer pain (lower back pain, joint pain, and neuropathic pain) who were continuously prescribed weak opioids for ≥1 month after initiating weak opioids between 2017 and 2022. Results Of 425,556 patients prescribed weak opioids, 42,514 patients (mean age: 50.1 years) were included. Most were prescribed ≤150 mg tramadol equivalent/day, and 21,405 (50.3%) were on weak opioids for lower back pain. The proportion of laxatives prescribed on the first day of weak opioid prescription was 6.7%; the cumulative prescription rate during the 12‑week follow-up was 13.6%. The most common laxatives during the first week were magnesium oxide (2,320 (66.6%)), sennoside (484 (13.9%)), and naldemedine (301 (8.6%)); at 12 weeks, these proportions were 55.2%, 13.1%, and 13.8%, respectively.​ The amount of weak opioids prescribed to patients without laxatives was lower than the standard dosage and was also lower than the amount prescribed to patients with laxatives. Conclusions This study showed that the actual prescription patterns of laxatives after initiating weak opioids in patients with chronic non-cancer pain were variable, depending on the duration after initiating weak opioids. The association between laxative use and weak opioid dosage indicates that OIC management may have a potential impact on pain management.