My son has a growth hormone deficiency and needs to take growth hormones by injection, which also need to be refrigerated. I just got a note from his doctor that states his medication is a medical need, that it must not be checked and must be carried on, and that it must be kept cold, along with a list of supplies that we must carry on with it. They gave us the same letter last time, and we had absolutely no issues with security. I don't know if they do the same thing for diabetics, but all we had to do was call the doctor and tell them we need a letter for plane travel and they mailed it to me. Makes me feel a lot better that if we get questioned about it we have supporting documentation.