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I am assuming that you are asking because the medication includes injections and not only oral medicine.
This depends slightly on the country but in most cases I have been involved with you bring the medication, syringes etc and a doctors prescription to the check in, and they will advice you from there.
Normally on the aircraft the crew will take care of your medication and the syringes as they will not let you keep it for yourself and when you need to medicate ( or your partner ) you will tell them and they will give you access to the medicine in a controlled manner.
I am assuming the flight in question is long enough that you need to medicate in the air.
Be aware that some airlines do not allow you to fly with them due to this condition, I have had a friend refused to fly with China Eastern a few years back as they do not allow needles on their aircraft even with a doctors note, note however that this was back in 2017 and might have changed.
As a recommendation it is always a good idea to call the airline and check what you need to prepare for this situation so that you dont get surprises on the day of travel.
Upvote:1
While Iβm not diabetic, there are a lot of self-help pages by interest groups - the ADA has US-centric air travel information for example.
In general, you should be allowed to take all necessary supplies (including syringes and larger amount of liquids) on the flight, though you need to submit them for inspection at security.
However, your question seems to be about at the customs channel when you arrive. If and what you have to declare depends on the destination country, because each had their own rules. You could check your governmentβs travel advisories, a travel guide or even with the embassy of your destination country.
Or you just declare the supplies at customs just in case.