Bill Ackman is hosting a call on Friday to talk about his huge money-losing bet on Valeant

Billionaire activist investor Bill Ackman, the founder of Pershing Square Capital, is hosting a conference call for investors on Friday morning to discuss his fund’s investment in Valeant Pharmaceuticals.

The call will take place at 9 a.m. ET. Ackman and other Pershing Square portfolio managers and analysts will take questions.

Since taking a position earlier this year, Pershing Square has potentially lost more than $US1 billion on paper on Valeant, the fund’s largest stock holding.

Since Wednesday, shares of the Canadian drug company have collapsed after California-based short-selling firm Citron Research published a report asking if Valeant was operating an Enron-like fraud.

Valeant’s share price has declined more than 38% since the report came out.

Valeant has categorically denied the allegations in the Citron report. The company hosted an all-hands call on Monday morning to address the allegations.

Ackman’s Pershing Square Capital Management currently owns 21,473,933 shares of Valeant. During Wednesday’s sell off, Ackman bought 2 million more shares, CNBC reported.

Pershing Square is the third-largest shareholder of Valeant.

Ackman first disclosed his position in Valeant on March 17, when the share price was $US200 per share. At that share price, the position was worth $US3.9 billion.

With his added shares from last week, Ackman’s position is worth $US2.36 billion at a closing share price of $US110.04 from Monday. That would represent a loss of around to $US1.5 billion.

Valeant’s stock has come under pressure in recent months. In late September, Democrats on the House Oversight and Government Reform Committee sent a letter to the committee’s chairman, Jason Chaffetz (R-Utah), asking him to subpoena the pharmaceutical company for documents related to price increases of acquired drugs.

At the Bloomberg Most Influential Conference earlier this month, Ackman said drug repricing was a very small part of Valeant’s business.

He later added: “Valeant has made a massive contribution to drug development, more so than almost any other company.”

In the spring of 2014, Ackman teamed up with Valeant to pursue a hostile takeover of Allergan, the maker of Botox. All of Ackman and Valeant’s offers were rejected.

At the time, Ackman didn’t own any shares of Valeant. He couldn’t own Valeant shares while working with the company on the takeover.

Ackman made around $US2.6 billion on his position in Allergan after the company was acquired by Actavis in a $US66 billion deal in November.

Pershing Square was the best-performing hedge fund last year, returning 40.4%. This year is a different story.

Pershing Square Holdings, the publicly traded vehicle for the fund, was down 11.2% for the year to October 20 before the Valeant collapse. The latest performance data for the fund is expected to come out Wednesday afternoon.

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