Why would insulin be a natural monopoly?It's the confluence of the low profit margin, high barrier to entry (FDA) and inelastic demand. The market does not support more than five or six players worldwide. It's like that for any generic.
That's common to all commodity medical supplies. Remember the IV saline shortage after Hurricane Maria took out the manufacturers on Puerto Rico? That doesn't need FDA approval (the facility does need inspection though), but you don't spin up a sterile bulk manufacturing facility in 6 months because of upfront costs that will take an eternity to recover.
You can only really make money in the US market
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You can fleece the US citizen only so much. Elizabeth Warren showed in 2004 how stretched he is, and it has only gotten worse since. The rest of the world may pay less but it's bigger. Also, when you can justify the cost to the public authorities it will be paid - note that a course of glecaprevir/pibrentasvir Hep C protease inhibitor is 26 kUSD in the US and a comparable 27 kGBP in Britain. A heap of money, but beats the liver transplant, both in cost and quality of life.
The bigger threat to pharma is the poor return on investment. Information technology pays off faster and with lower risk. Goldman Sachs suggested the government step in, they are the only ones with big enough pockets. The suggestion is sound.