A P2X 4 receptor antagonist such as paroxetine, a diazepinedione derivative having the following formula (IX) is used as an agent for preventing or treating neuropathic pain associated with Guillain-Barré syndrome: wherein R 1 is hydrogen, a C 1-8 alkyl group, or the like； each of R 2 and R 3 is hydrogen, a C 1-8 alkyl group, or the like； each of R 4 and R 5 is hydrogen or the like； and W is a five-membered or six-membered heterocyclic ring optionally having one or more substituents and comprising one to four nitrogen atoms as the members of the ring.
