What drug was a medical breakthrough in 1921 to treat diabetes?

I take 6 insulin shots daily and thank God for it!

Banting was one of life's unsung heroes, given the course of history and his lack of specialty - yet still got it right.

I. M. PRE. DIABETIC. MY. HUSBAND. & DAD. WERE. DIABETICS. TOO. THEY. TOOK. INSULIN SHOTS. EVERYDAY

My granddad has diabetes and takes insulin shots

herb198220, I'm guessing in Canada where Banting was from