Hedge fund manager and activist shareholder Bill Ackman has bought 2 million new shares in Valeant at an estimated total cost of $230 million. The buy is said to have increased his interest in the Canada-based drugmaker run from the US to roughly 21 million shares worth around $2.5 billion.

Ackman reportedly purchased the shares shortly after a research note from short seller Citron Research caused a furor on the market. This led the paper to plunge, losing $17 billion of its value in only two days.

The note drew attention to Valeant’s earlier disclosure that it had purchased an option to acquire Philidor, one of a number of specialty pharmacies suspected of creating “phantom sales” and had been consolidating the company’s results in its own financial reports. The company later sought to clarify the details.

US federal prosecutors meanwhile have launched an investigation into Valeant’s pricing policies, focusing primarily on financial assistance to patients who are unable to afford the company’s drugs. As laws forbid giving aid to patients directly, the funds are routed through independent foundations.

The Canadian drugmaker also has been criticized for a series of so-called buy and raise deals in which it has acquired an older drug and jacked up the price, in particular for two cardiovascular drugs that have seen hikes of 55% and 212% respectively.

Valeant announced late Thursday that it planned to hold a conference call on Oct. 26 to address the latest allegations against it.