Oligopoly - Why is insulin so expensive?

Insulin is an essential drug for diabetics, but the price has increased so dramatically. Why? You would think that the absence of patent protection would reduce the market price of insulin.

Well, insulin is only produced by three firms in the US - who claim to set prices independently - but as a good economist with an understanding of business behaviour in an oligopoly, you might think differently.

This is a fantastic look at the nature of the markets and a really rather worrying clip.