The "appropriate" answer has already been given, in my opinion.


Consult the Japanese Embassy/Consulate on the matter and follow their guidance. And/or consult a lawyer who is throughly familiar with Japanese law on smuggling and illegal drugs. And/or ask your physician in your home country if there is another medicine that will achieve the desired effect that is also legal to bring into Japan.

If the OP [or someone else] is caught smuggling and receives particularly harsh punishment it won't make a difference what the chances are of, or that someone else received, a lesser punishment.

As others have said, it is about risk tolerance on the would be smugglers part.