Valeant Pharmaceuticals, whose stock has fallen 73 percent this year amid U.S. investigations of its business and accounting practices, announced Monday that CEO Mike Pearson is leaving. The board ousted Pearson after a series of weekend phone calls, a decision that "was not mutual" according to a person familiar with the situation.
The same source tells CNBC, Valeant's board informed Pearson of the action it was taking — to immediately initiate a search for the next CEO, and that he was no longer in the company's long-term plans.
In a Monday statement, the board also announced that activist investor Bill Ackman is joining the board. Former CFO Howard Schiller refused to leave the board to make room for Ackman.
Shares of Valeant closed up 7 percent on Monday. Over 9 million shares were traded in the first 10 minutes of trading.
Valeant said that Pearson will stay on as CEO until his successor is found.