The pharmaceutical giant AbbVie (ABBV  ) has been taking advantage of the patent system for roughly five years to protect its monopoly over one of the top-selling prescription medications in the United States. AbbVie's patent on Humira should have expired in 2016, but it used the system to block a generic version of the drug from being introduced until this year.

A generic version of Humira had already been approved by regulators before its patent expired, but AbbVie sued competitors and applied for an additional 311 Humira-related patents to legally ensure the drug remained unrivaled. If a generic drug had gone on the market in 2016 as expected, the price of Humira would have dropped, saving patients billions of dollars.

Instead, AbbVie has gone on to raise the drug's price by an additional 60%, raking in $114 billion in revenue from Humira just since the end of 2016. According to one study, Medicare spent an additional $2.2 billion on Humira from 2016 to 2019 thanks to AbbVie's dominance of the market. Patients interviewed for the study reported delaying retirement or going without treatment due to the high out-of-pocket price of the drug.

Next week, the same generic drug that received regulator approval years ago will finally become available, along with up to nine other knock-off versions. Thanks to settlements with competitors for earlier suits, AbbVie will still make royalties off of the competing drugs.

While AbbVie is far from alone in its manipulation of the pharmaceutical patent system, it has gone farther than most, according to experts.

"Humira is the poster child for many of the biggest concerns with the pharmaceutical industry," a drug pricing expert at Washington University, Rachel Sachs, told The New York Times. "AbbVie and Humira showed other companies what it was possible to do."

There are two primary ways that AbbVie and other pharma giants like Merck (MRK  ) and Amgen (AMGN  ) use the patent system to block competition. First and most simply, they may sue and later settle with competitors for allegedly violating their patents, whether or not the case has merit. As a part of the settlement agreement, competitors are required to delay the introduction of the competing drug.

On the other hand, some companies, like AbbVie, file hundreds of nearly identical patents on treatments related to the original drug in order to extend protections. For example, one of Humira's early patents stated that it could be used to treat a kind of arthritis called ankylosing spondylitis, but another patent for Humira's ankylosing spondylitis treatment was later approved because it included specific dosages for the condition. As a result, Humira's patent protections were extended.

One of AbbVie's own top executives, Bill Chase, admitted in 2014 that the company's patent strategy regarding Humira was meant to "make it more difficult for a biosimilar to follow behind."

Biosimilars, in contrast to generic drugs, are non-identical competitors for complex biologic medicines. Biosimilars were first established in the U.S. pharmaceutical industry by the 2010 Affordable Care Act in an effort to bring down drug prices.

While other countries have seen the positive cost-cutting effects of biosimilars, pharmaceutical companies in the U.S. have used the patent system to stop biosimilars from challenging their market control.