In another deal between the two companies that could be worth more than $1 billion, Abbvie Inc. is buying Gilgamesh Pharmaceuticals Inc.’s lead candidate bretisilocin (GM-2505) for up to $1.2 billion, including an undisclosed up-front payment and development milestones. Privately held Gilgamesh has the psychedelic compound for treating moderate to severe major depressive disorder in a phase II study.