Hi. Some over the counter (OTC) drugs are allowed, if within a certain amount, to be carried into Japan. However, these must be for your own personal use only and must not exceed and not more than a month's supply, otherwise, you'll be troubled to get a Medicine Import Certificate. In any case, since it is just a motion sickness medicine, it normally is allowed by the authorities. Moreover, if it helps, you may also purchase these meds at drugstores in Japan during your stay.