Mallinckrodt's (MNK) - Get Report  long history of raising prices on its most critical drug, Acthar Gel, could prove a liability for shareholders as watchdogs continue adding new pressures across the industry.

Senate regulators recently have been gunning for drugmakers with a record of hiking drug prices, such as Wednesday's announcement by a Senate special committee that is requesting answers over Mylan's (MYL) - Get Report  "drastic price increase" on its allergy treatment EpiPen, a drug whose prices have risen 480% to roughly $600 since 2008.

Mylan was quick to slash its prices Thursday after Democratic presidential nominee Hillary Clinton -- who's been no stranger to attacking Big Pharma price hikers -- called Mylan's policies "outrageous" and "troubling" examples of putting corporate shareholders ahead of patients. Mylan said in a statement it will effectively reduce out-of-pocket costs by about 50% for EpiPen patients with "savings cards."

And the same committee also subpoenaed beleaguered drugmaker Valeant Pharmaceuticals (VRX)  in April -- a company Clinton has also accused of "price gouging" -- with the hearings culminating in Valeant's ousted CEO Michael Pearson apologizing for putting shareholder interests above patients.

"One day the media will turn its attention on Mallinckrodt and understand how they are gaming the system," short-seller Andrew Left said in a Wednesday phone interview withReal Money.

Left's case is that the price of Acthar Gel, which is used to treat multiple sclerosis and lupus, has been boosted to exorbitant levels, and is not going to realize the gains expected from analysts at firms like Piper Jaffray, which boosted its price target on Mallinckrodt to $112 from $103 and reiterated its Outperform rating.

Acthar is Mallinckrodt's top-selling product, comprising 31% of the company's second-quarter net sales, based on its most recent filing with the Securities and Exchange Commission. As Left puts it: "The company lives and breathes on Acthar."

Left, who manages the bear-focused Web newsletter Citron Research, feels Acthar is in precariously worse shape than the EpiPen, which "has been tested and it works," as opposed to Acthar, which he argues has never received a meaningful independent clinical trial since the drug's 1952 approval. At the time, the FDA tested more for safety than efficacy by today's standards.

Acthar prices are today listed at upward of $34,000 a vial, up from reports of about $50 in the early 1990s, and the drug has been widely cited among those that have recently drawn public ire from patients and lawmakers.

Mallinckrodt responded Thursday in an email to Real Money noting, "Mr. Left continues to recycle allegations about Mallinckrodt and its products that aren't supported by fact," highlighting that Mallinckrodt net sales for its fiscal third quarter climbed 11% "driven entirely by volume" across the company's "well diversified portfolio of highly durable Specialty Brands."

The drugmaker noted its growth in volume supported by investments in "new clinical and health economic data," and that Mallinckrodt has made nearly 20 data presentations for Acthar Gel over the period.

"There is ample data and experience to demonstrate the effectiveness of Acthar in seriously ill patients, and when compared with some of the alternative treatments, Acthar can be cost effective," the company concluded.

Acthar's exponential rise in price occurred while under the drug portfolio of Questcor, which was acquired by Mallinckrodt for $5.6 billion in April 2014. Questcor managed to keep Acthar prices on the rise by purchasing the rights, in 2013 for $135 million, of competitor Synacthen, which produced a synthetic version of the anti-inflammatory drug that threatened to curb pricing strategy, Left said.

Martin Shkreli -- the former CEO of MSMB Capital who was arrested on charges of using funds from his drug company Retrophin to pay off MSMB investments -- saw the benefits of this, hoping to compete against Questcor, according to Left. "When he had Retrophin, he tried to buy the synthetic form of Acthar, and then in the 11th hour, Questcor bought the synthetic of their own drug," he added.

Meanwhile, Piper Jaffray analysts, in their Wednesday rating report, argued that critics' attempts to demonize the legitimacy of Acthar prices are unfounded, and that the drug is likely to continue servicing as a chief growth driver. Analysts note that while access to Acthar is "still tightly restricted," there is "greater standardization of Acthar coverage among the myriad payers, generally making the process of getting an Acthar prescription filled more predictable and in our view making it more likely that physicians/practices will be more consistent writers of Acthar Rx's."

Mallinckrodt shares closed down 4.7% Wednesday, also off a Wednesday announcement that the company is selling its nuclear-imaging businesses to Virginia-based IBA Molecular for roughly $690 million. Shares are down slightly Thursday to $78.75.

"I am not short the stock," Left concluded. "But there will be plenty of time to short the stock when the company gets the attention from Congress it deserves."

Editor's Note: This article was originally published at 8:39 a.m. on Real Money on Aug. 25.