[…] Insulin is also unique in its market structure: a persistent oligopoly both nationally and globally, in particular with respect to the prices of analog insulins. Only three companies—Novo Nordisk, Sanofi, and Eli Lilly—provide insulin the United States market, despite the existence of several other manufacturers globally.
It’s not a generic drug there:
https://academic.oup.com/jlb/article/7/1/lsaa061/5918811