BILL ACKMAN: 'Of course' I regret Valeant

Activist investor Bill Ackman says "of course" he regrets investing in Valeant, the former stock market darling that's been hit with SEC investigations, Senate probes, and a precipitous decline in its stock price.

"There's been a lot of brain damage in the last five weeks working with the board," Ackman said in an interview with CNBC's Scott Wapner on Monday.

Ackman joined Valeant's board in March as Valeant's CEO, Mike Pearson, announced his departure from the firm.

Ackman was also asked whether he regretted not selling his shares in Valeant at any point, rather than getting even further involved with the firm by joining its board.

"Any price would have been better" than Valeant's current price of about $31, he responded.

Valeant's stock has plunged about 86% in the past year and almost 70% since October.

Warren Buffett and Charlie Munger called Valeant a "Wall Street scheme," enormously flawed, and "a sewer" at the annual Berkshire Hathaway shareholder meeting over the weekend.

Valeant last week released its 10-K report after multiple delays. It revealed that Valeant misstated financials in the first quarter of 2015, which reduces revenue by $21 million but actually increases profits by $24 million.

It also disclosed the company is undergoing investigations in North Carolina, New Jersey, Massachusetts and New York.