Scott Alexander wrote a whole article on the difficulties in bringing competitors to out of patent drugs to the US market:<p><a href="http:&#x2F;&#x2F;slatestarcodex.com&#x2F;2015&#x2F;09&#x2F;24&#x2F;the-problems-with-generic-medications-go-deeper-than-one-company&#x2F;" rel="nofollow">http:&#x2F;&#x2F;slatestarcodex.com&#x2F;2015&#x2F;09&#x2F;24&#x2F;the-problems-with-gener...</a>