Nausea and vomiting are common side effects due to opioid therapy, and may greatly impede the quality of life of cancer patients. A preventive method for nausea and vomiting has not yet been established. We developed a clinical pathway(CP) for cancer pain management in which prochlorperazine is used for the prevention of nausea and vomiting caused by opioids. We have shown that this CP is effective for relieving cancer pain. In this study, we investigated the efficacy prochlorperazine has for preventing nausea and vomiting caused by opioids in patients treated with the CP. The incidence of nausea and vomiting of those patients was 15. 8% which was lower than the results of other previous clinical trials. However, we could not show the effectiveness of prochlorperazine. Prochlorperazine, which is a dopamine D2 receptor antagonist, may show limited utility for the prevention of nausea and vomiting; however, in opioid therapy, histamine receptor(H1)prevention is also important.