As we said above, for many years, the FAA did not extend Special Issuance consideration to insulin-treated pilots, so first and second-class medical certificates were simply not an option for type I diabetics, only type II.
Things started to change in April 2015 however, when the FAA revised its position to state that it would provide consideration "on a case by case basis" for pilots applying for first and second-class certifications, however, it didn’t actually grant any certificates.
Then, on November 7, 2019, the FAA published a notice in the Federal Register announcing a new protocol for evaluating those with insulin-treated diabetes applying for first and second-class medical certificates.
This process is still very much reliant on a case-by-case assessment of those with diabetes, however, this is thought to be the most medically and legally appropriate approach to considering whether or not a person is in a fit state to fly an aircraft.
However, the U.S. is not at all the first country to make these changes.
Since 2001, Canada has been allowing some pilots with insulin-treated diabetes to fly commercial flights, while in 2012, the UK also made a similar move, approving a protocol that allowed pilots with insulin-treated diabetes to engage in airline transport and commercial operations.