Pershing Square Capital Management, the hedge fund of billionaire US activist investor Bill Ackman, has trimmed its stake in Canada-headquartered Valeant Pharmaceuticals from almost 10% in November to 8.5%. In a regulatory filing, Pershing Square said it had sold 5 million shares in the beleaguered drugmaker to “generate a tax loss for investors.” Valeant’s share price was down an estimated 20% at the end of December as the company’s business practices came under scrutiny from the US Congress.

Altogether, the shares have descended by around 60% from the lofty peaks they rose to in summer 2015, reports said.

The Congressional investigation came after short-seller Citron Research criticized Valeant for its ties to controversial mail order pharmacy Philidor which marketed the company’s dermatology drugs.

Valeant also attracted negative press after the Wall Street Journal last spring reported that the company had hiked prices for two cardiology drugs by 25% and 212% respectively after buying rights to the medications earlier in the year. Along with dermatology, the drugmaker, which is run from the US despite being based in Canada, specializes in eye care and neurology drugs.

Meanwhile, Valeant has confirmed that its CEO, Michael Pearson, is on medical leave. Reports said the 56-year-old was suffering from severe pneumonia. Pearson has headed the company since 2008. The company’s board of directors has created what is being called an “office of the chief executive” to run it in the interim.