Some medications available through prescription or over the counter in the U.S. are prohibited in Japan and cannot be brought into the country.
Heroin, cocaine, MDMA, opium, cannabis and stimulant drugs, including some prescription medications such as Adderall, are prohibited.
There are no exceptions in bringing these prohibited medications into Japan, even if the medication is legally obtained in another country.
The health ministry says anyone who intends to enter Japan carrying narcotics, including morphine, codeine, oxycodone, pethidine and hydrocodone for medical purposes, must obtain advance permission via an application form and medical certificate from a doctor outlining the need for the narcotics, the drugs' names and the quantities prescribed. Only up to a month's supply of prescription medicine can be brought into Japan.
For more information, refer to entries on the websites of the U.S. Embassy (japan.usembassy.gov/mobile//e/acs/tacs-medimport.html) and Japan's Health, Labor and Welfare Ministry (www.mhlw.go.jp/english/policy/health-medical/pharmaceuticals/01.html)