Citing antitrust considerations, the group of six filed an amended complaint backing the FTC’s opposition to the transaction on grounds it would give Amgen "monopoly positions" for medicines used to treat thyroid eye disease and chronic refractory gout.

In a statement, California Attorney General Rob Bonta said the acquisition would be “dangerous for the future of medicine, dangerous for innovation and research, and most importantly, dangerous for sick people in need of often lifesaving drugs.”

Washington Attorney General Bob Ferguson said the state had joined the lawsuit because "monopolies harm consumers" and the merger could allow Amgen to "dominate" prescription drug markets.

Amgen has had its sights trained on Horizon for some time, finally unveiling its plans in December 2022. Since being announced, the acquisition drive has been on a rocky road, with the FTC twice asking the company for more information.

In response to a temporary restraining order obtained by the FTC, Amgen last month agreed not to close the deal before Oct. 31 or the second business day after the court rules on the trade watchdog’s request to block it. A US district judge has set Sept. 11 as the date to hear the request.

Initially, the companies said they hoped to conclude the transaction in the first half of 2023.

Author: Dede Williams, Freelance Journalist