There is no market concept that explains why the drug manufacturers charge patients in the US so much more than they charge in other places.
Especially since they get so much US government aid in the process.
Patents. They are effectively a government created monopoly, meaning no competition is allowed. Furthermore, strict and expensive FDA regulations reduce competition further and only the few who can afford to pass them can supply the drug (and the cost of passing them must be recouped from the patients who use the drug). Finally, there is a general ban on imports unless they have passed said strict FDA regulations and approval process, reducing competition even further. Note that this is all contrary to the statement I made:
With robust competition