Its codeine for me too - for my chronic cough I take a massive 2 ml per day! I was not taking this medication for earlier trips, and I did apply for the permit for my first trip with codeine in 2020 and it was a total PITA, including having to physically post my application and supporting paperwork to them once I arrived in Japan - the permit was processed by an emailed copy of the application and supporting paperwork, but "not valid" unless I mailed the originals from Japan. Mailing from Australia was not acceptable. Then when I arrived, airport (HND) staff/customs/immigration/various officials did not know what to do with me. I spent more than 45 minutes waiting while phone calls were made. They did not have a copy of the permit and asked to photo copy my own permit. They did not at any point ask to see the medication. Plus it was stressful waiting for the application to be approved, which did not come through until close to departure date (apparently this is normal) but it stressed me out as I need to make an alternative medication cough management plan if I can't have my codeine syrup. I also received considerable huffing and puffing from the travel companions as it took a lot of time, caused us to almost miss our bus connection, and in my wider circle people have paid out on me for being a goody two shoes as they have all taken something on the non-approved list in without trouble.
Based on that, I did not bother to apply for the permit for the 2023 and 2024 trips, with the plan that I would just apologise for my overisght and just surrender the codeine at the border. I expected they might be a bit cross but nothing more. I know it was a risk, and contrary to their rules, but that was the risk assessed decision that I made at the time.
But now after reading this experience of
@drron, I am envisaging being arrested and taken off for interrogation and detained. I will definitely be applying for the permit. And yes don't flame me, I already know I should have applied each time.