All drugs are regulated by the FDA, even if a drug patent is expired you need to get FDA approval to sell a generic version, which would cost millions. The only way around this, is if you market your product as not for human consumption or make some obscure research drug and market it as a health supplement.
Of course the latter two eventually will get you in deep shit with the FDA.
...or at least meet the legal definition of making it oneself? Like the "build your own AR-15" kits where 99% of the work is already done, but for insulin?
Of course the latter two eventually will get you in deep shit with the FDA.