In December, investors learned of Amgen Inc.'s $28 billion bid for Horizon Therapeutics PLC. But a clue to a potential deal emerged months earlier, when insiders at Horizon Therapeutics stopped selling stock.

This year was supposed to be a big one for healthcare deals. However, the pandemic has put a damper on many of these plans.

Data compiled by Bloomberg revealed that companies announced $3.5 trillion in deals in 2022.