Checked against UN INCB controlled substance lists and Japan rules.
Codeine is a narcotic in Japan, so the ordinary import-certificate route does not cover it: you apply to the Narcotics Control Department for permission before you travel. One threshold decides many cases - preparations containing 1% or less of codeine are excluded from control, which is why some low-dose cough preparations pass and prescription-strength ones do not.
codeine contains a substance on the UN International Narcotics Control Board lists. Most countries that signed the UN drug conventions expect you to carry a prescription and declare it.
Apply for approval from the destination's health authority well before you travel. Carry the prescription, a doctor's letter and the original packaging.
Official source for Japan: www.mhlw.go.jp
There is no counter at the airport that issues it. The application process, the lead time and what to attach — and a letter template for your prescriber.
Not legal or medical advice. Rules change and depend on dose, form and quantity. Always confirm with the Japan embassy or health authority before you fly. We never tell you a medicine is "safe" to carry.