[yuriyuri]

I don't know anything about what you are allowed to take to Japan in terms of medicine, but I remember the second time I went to Japan was with a friend who needed an inhaler.
He had to put it in a plastic bag and was allowed to continue with no problems.

In my bag I had Paracetamol, Lemsip and some other tablets that I can't remember the name of right now.
They took them out of the bag and didn't know what they were, so I just explained that it was medicine for headaches etc, and that was good enough for them.

Of course it would be best to find out, but I thought I would just let you know about my own experience with taking over the counter medicines with me.
Of course none of it was prescribed medicine, but as others have said I heard it is best to take all prescriptions with you.