Opioid-induced constipation(OIC)occurs with high frequency in patients with cancer undergoing pain treatment using opioids. Osmotic or irritant laxatives are usually used to prevent OIC. Recently, naldemedine has become operational for OIC. Although naldemedine achieved the desired effect, diarrhea is a little feared from the results of clinical phase III study(V9236 clinical trial). We herein report the use of naldemedine to alleviate diarrhea and expect the improvement of the quality of the bowel habits in outpatients with cancer undergoing pain treatment using opioids.