A 60-year-old woman was treated with oxycodone extended-release tablets for the cancer pain due to cervical cancer, and oxycodone was continued for abdominal pain due to radiation enteritis, laparotomy, small bowel obstruction, and constipation even after the cancer had been cured with chemoradiotherapy. The patient experienced severe drowsiness, and the opioid analgesics dose was gradually reduced. The dose was reduced by switching from oxycodone extended-release tablets to morphine powder. The patient’s drowsiness, constipation, and abdominal pain improved with reduction in opioid dosage, but she developed malaise, sweating, and agitation. These symptoms improved with morphine powder; thus, she was diagnosed with opioid withdrawal syndrome. We attempted to further reduce the dose gradually over a period of four years, but withdrawal symptoms reappeared when morphine powder was discontinued. Therefore, at present, we are administering her small doses of morphine powder. Though inappropriate use of opioid analgesics should be strictly avoided, in some cases, long-term use under careful specialist supervision may be necessary before discontinuation of opioid analgesics.