The following is taken from the US Embassy’s website: http://japan.usembassy.gov/e/acs/tacs-medimport.html. Please refer to it for the most recent information concerning importation of medicine into Japan.
Decisions on what medications may be imported legally into Japan are made by the Japanese Government, and unfortunately the limited information we have available at the American Embassy and our Consulates does not include comprehensive lists of specific medications or ingredients. This information is available only from the Japanese authorities, and is subject to change.
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. Up to a two-month supply of allowable over-the-counter medication and up to a four-month supply of allowable vitamins can be brought into Japan duty-free.
Some US prescription medications cannot be imported into Japan, even when accompanied by a customs declaration and a copy of the prescription. Japanese customs officials have detained travelers carrying prohibited items, sometimes for several weeks. Japanese customs officials do not make on-the-spot “humanitarian” exceptions for medicines that are prohibited in Japan.
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. Travelers who must carry more than one month’s supply, or are carrying syringes, may be required to fill out a customs declaration form before entering Japan. To obtain the customs declaration form before you leave, or for more information on taking medication into Japan, contact the Consulate General of Japan’s Economic Section by phone at 415-777-3533 or on the internet at http://www.sf.us.emb-japan.go.jp/en/e_m08_01_16.htm#6. The American Embassy and the Consulates in Japan do not stock these forms.
Japanese physicians can often prescribe similar, but not identical, substitutes to medicines available in the US. A list of English-speaking medical facilities throughout Japan is available on the US Embassy’s website at http://japan.usembassy.gov/e/acs/tacs-7119.html. A Japanese doctor, consulted by phone in advance, is also a good source of information on medications available and/or permitted in Japan.
Some popular medications legal in the US, such as Prozac and Viagra, are sold illegally in Japan on the black market. You are subject to arrest and imprisonment if you purchase such drugs illegally while in Japan.
Since ADHD still is not well known in Japan as it is in the United States, medications for it are not widely available. Please refer to the US Embassy and Japan Ministry of Health, Labor and Welfare’s websites for more information.
Other Government of Japan sources of information are included on the web site of the Compliance and Narcotics Division, Pharmaceutical and Food Safety Bureau, Ministry of Health, Labor and Welfare at www.mhlw.go.jp/english/topics/import/index.html under the heading “Importing or Bringing Medication into Japan for Personal Use.”