There is no reason why a person with insulin-dependent diabetes cannot fly. However, it is best to discuss with your doctor how to manage your insulin needs. Passengers with diabetes do not require a medical agreement to travel on Ryanair flights as long as their condition is stable, and they are able to administer their own medical treatment.
If you are unable to administer your own treatment, you should bring someone with you to provide the necessary assistance. Passengers must be provided with a letter from their doctor confirming their need to carry syringes, needles, and medication in the aircraft cabin. Since airport security checks are not Ryanair's responsibility, you will always need to have a doctor's letter stating that you need to carry "sharp" objects on board an aircraft. Passengers should keep and then discard any syringes, needles or medication after leaving the aircraft as these should not be disposed of onboard.