In 2016, a blockbuster drug called Humira was poised to become a lot less valuable.

The key patent on the best-selling anti-inflammatory medication, used to treat conditions like arthritis, was expiring at the end of the year. Regulators had blessed a rival version of the drug, and more copycats were close behind. The onset of competition seemed likely to push down the medication’s $50,000-a-year list price.

Instead, the opposite happened.

Through its savvy but legal exploitation of the U.S. patent system, Humira’s manufacturer, AbbVie, blocked competitors from entering the market. For the next six years, the drug’s price kept rising. Today, Humira is the most lucrative franchise in pharmaceutical history. [...]

Over the past 20 years, AbbVie and its former parent company increased Humira’s price about 30 times, most recently by 8 percent this month. Since the end of 2016, the drug’s list price has gone up 60 percent to over $80,000 a year, according to SSR Health, a research firm.

One analysis found that Medicare, which in 2020 covered the cost of Humira for 42,000 patients, spent $2.2 billion more on the drug from 2016 to 2019 than it would have if competitors had been allowed to start selling their drugs promptly. In interviews, patients said they either had to forgo treatment or were planning to delay their retirement in the face of enormous out-of-pocket costs for Humira. [...]

AbbVie and its affiliates have applied for 311 patents, of which 165 have been granted, related to Humira, according to the Initiative for Medicines, Access and Knowledge, which tracks drug patents. A vast majority were filed after Humira was on the market.

Some of Humira’s patents covered innovations that benefited patients, like a formulation of the drug that reduced the pain from injections. But many of them simply elaborated on previous patents.

For example, an early Humira patent, which expired in 2016, claimed that the drug could treat a condition known as ankylosing spondylitis, a type of arthritis that causes inflammation in the joints, among other diseases. In 2014, AbbVie applied for another patent for a method of treating ankylosing spondylitis with a specific dosing of 40 milligrams of Humira. The application was approved, adding 11 years of patent protection beyond 2016. [...]

AbbVie has been aggressive about suing rivals that have tried to introduce biosimilar versions of Humira. In 2016, with Amgen’s copycat product on the verge of winning regulatory approval, AbbVie sued Amgen, alleging that it was violating 10 of its patents. Amgen argued that most of AbbVie’s patents were invalid, but the two sides reached a settlement in which Amgen agreed not to begin selling its drug until 2023.

Over the next five years, AbbVie reached similar settlements with nine other manufacturers seeking to launch their own versions of Humira. All of them agreed to delay their market entry until 2023. [...]

Even now, as AbbVie prepares for competitors to erode its Humira sales in the United States, the company will have a new way to make more money from the drug. Under the terms of the legal settlements it reached with rival manufacturers from 2017 to 2022, AbbVie will earn royalties from the knockoff products that it delayed.

The exact sizes of the royalties are confidential, but analysts have estimated that they could be 10 percent of net sales. That could translate to tens of millions of dollars annually for AbbVie.