Bill Ackman lost $321 million on Monday

Bill Ackman

Bill Ackman’s holdings in Valeant Pharmaceuticals cost him $321 million in a single day.

Shares of the drugmaker fell more than 18% yesterday, the biggest decline since October, according to data compiled by Bloomberg.

T. Rowe Price Group Inc. had a one-day drop of about $324 million, and William Ackman’s Pershing Square Capital Management gave up $321 million.

The company’s biggest owner, investment firm Ruane Cunniff & Goldfarb, lost an estimated $525 million after the price collapse.

Those loss estimates assume that all three company’s are carrying the same number of shares they listed in their most recent regulatory filings.

The company’s share price fell apart after it withdrew a financial forecast, delayed the release of fourth-quarter results, and confirmed a probe by the U.S. Securities and Exchange Commission.

Valeant shares are down nearly 75% since August and 35% in 2016.

Shares at the company are down more than 5% at 12:05 PM EST on Tuesday.

Valeant Pharmaceuticals

The pharmaceuticals giant has come under fire for its rapidly rising drug prices, accounting and distribution practices.

The company announced on Sunday night that Chief Executive Officer Michael Pearson would give up his chairman title and return after a two-month medical leave.

“We are delighted that Mike’s health has recovered and he has returned as CEO so that he can now work on behalf of the company and shareholders,” Ackman said in a statement Monday to CNBC.

Ackman believes all controversies surrounding the company will be resolved “in short term.”