The Federal Trade Commission (FTC) said Tuesday it will sue to stop Amgen’s $27.8 billion acquisition of Horizon Therapeutics.

The FTC said in the complaint that Amgen would be able to leverage its position with insurance companies and pharmacy benefit managers wanting access to its blockbuster drugs, while pressuring them into favorable terms for Horizon's two key products – the fast-growing thyroid eye disease treatment Tepezza and gout drug Krystexxa.

In response, Amgen issued a statement saying it was disappointed by the FTC decision and that it believed it had "overwhelmingly demonstrated" that the deal had no legitimate competitive issues.

Meanwhile, FTC Bureau of Competition Director Holly Vedova said: "Rampant consolidation in the pharmaceutical industry has given powerful companies a pass to exorbitantly hike prescription drug prices, deny patients access to more affordable generics, and hamstring innovation in life-saving markets."

Amgen announced plans to buy Horizon in December, saying that its rare disease drugs would offer it some protection from the drug pricing provisions of the Inflation Reduction Act, which are aimed at drugs most widely used by the government's Medicare health plan.

Reuters contributed to this report.