The present invention is intended to provide a novel pharmaceutical agent having an excellent preventive effect on post-stroke RSD. The present invention provides an agent for preventing the onset of post-stroke RSD, comprising natural calcitonin or a calcitonin derivative as an active ingredient. The present invention is also intended to provide a method for preventing the onset of post-stroke RSD, comprising administering natural calcitonin or a calcitonin derivative and use of natural calcitonin or a calcitonin derivative for producing an agent for preventing the onset of post-stroke RSD.
