The trillion-dollar drug industry operates on a grand bargain. If you invent a wonder pill, you get a patent and thus a monopoly. The catch is that the patent must one day expire, opening the door to cheap generics and forcing inventors back to the well to start the cycle all over again.

But it can be quite hard to say goodbye to a monopoly and the riches it brings. And so drug companies tend to get creative in the waning days of patent exclusivity, stretching the law to translucent lengths in the name of protecting profits. That became quite evident (again) last week, when Allergan surprised the pharma world by announcing it had sold patent rights on a lucrative eye drug to a Native American tribe to avoid facing certain legal challenges by generics.