Last week, Allergan sold patent rights to a big-selling eye drug called Restasis to a Native American tribe, which is protected from the lawsuits generic drugmakers use to challenge pharmaceutical patents. As STAT News reports, it’s just one of several tricks big pharma companies use to maintain a monopoly on a product.

Sometimes the tactics involve bringing a new product to stave off competition from generics, like an extended release version of the same drug, then pulling the original from the market and give prescribers no choice but to use the new product. In other instances, companies just keep patenting new changes to the product, like Mylan patenting the additional of a push button to its EpiPen autoinjector.

Allergan’s strategy is a new one, however, but that could lead to a legal battle which could “completely subvert the grand bargain on which the industry operates.”

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