Late to the discussion here but as I am also a diabetic I have never been questioned about my insulin or syringes but now that I am on a pump and CGM it is a new PITA to get my equipment rescued from being sent through the carryon scanner-not sure I save much time with TSA pre check anymore.

My last transit through Heathrow was waaaaay back in 9/2018 in First security and no one had an issue with my paraphernalia.

For those concerned about buying/bringing a sharps container for disposal, an empty plastic water bottle works well to store sharps in and then bring them home or later find a sharps container in an airport.