Found the following that should help.
You may not be from the US but I'm sure it's the same whatever country you come from.
Confiscation of Prescription Drugs and Other Medication: The Japanese government decides which medications may be imported legally into Japan, and the limited information available at the Japanese Embassy and its consulates does not include comprehensive lists of specific medications or ingredients.
Up to a two-month supply of allowable over-the-counter medication and up to a two-month supply of allowable vitamins can be brought into Japan duty-free. However, it is illegal to bring into Japan some over-the-counter medicines commonly used in the United States, including inhalers and some allergy and sinus medications. Specifically, products that contain stimulants (medicines that contain pseudoephedrine, such as Actifed, Sudafed, and Vicks inhalers) or codeine are prohibited. Generally, up to one month's supply of allowable prescription medicine can be brought into Japan. Travelers must bring a copy of their doctor's prescription as well as a letter stating the purpose of the drug. However, some U.S. prescription medications cannot be imported into Japan, even when accompanied by a customs declaration and a copy of the prescription. Travelers should not mail prescription medicines, including insulin and injectors, without obtaining an import certification called “Yakkan-Syoumei” from the Ministry of Health, Labor and Welfare. Please see more information on importing medicines into Japan.
Japanese physicians can often prescribe similar, but not identical, substitutes for medicines available in the United States. A Japanese doctor consulted by phone in advance can also be a good source of information on medications available and/or permitted in Japan. See the list of English-speaking medical facilities throughout Japan on our website. Some popular medications that are legal in the United States, such as Prozac and Viagra, are sold illegally in Japan on the black market. You risk arrest and imprisonment if you purchase such drugs illegally while in Japan.
Persons traveling to Japan carrying prescription and non-prescription medications should consult the Japanese Embassy, or a Japanese consulate, in the United States before leaving the United States. to confirm whether they will be allowed to bring the particular medication into Japan.
this should also help, includes application for Yakkan-Syoumei
http://kouseikyoku.mhlw.go.jp/kantos...nes_070618.pdf