To provide a cancer pain therapeutic and/or prophylactic agent which can be administered to a patient for a long period of time from the early stage to the final stage of the cancer pain therapy, instead of conventional non-opioid analgesic agents or opioid analgesic agents. The cancer pain therapeutic and/or prophylactic agent containing, as an active ingredient, a 1,5-benzodiazepine derivative represented by formula (1): (wherein R 1 represents a C 1-6 alkyl group, R 2 represents a phenyl group or a cyclohexyl group, and Y represents a single bond or a C 1-4 an alkylene group) or a pharmaceutically acceptable salt thereof.本發明提供一種癌症疼痛治療藥及/或預防藥,其可代替先前之非類鴉片止痛藥及類鴉片止痛藥,自癌症疼痛治療之初始階段至最終階段長期持續服用。本發明之癌症疼痛治療藥及/或預防藥係將通式(1)所表示之1,5-苯二氮呯衍生物或其藥學上容許之鹽作為有效成分者:(式中,R1表示C1-6烷基,R2表示苯基或環己基,Y表示單鍵或C1-4伸烷基)。
