(Reuters) — Indivior PLC lost three-quarters of its stock market value on Wednesday and former parent Reckitt Benckiser Group PLC also fell after the U.S. Justice Department accused the British drugmaker of illegally boosting prescriptions for its blockbuster opioid addiction treatment.

An indictment filed in federal court in Abingdon, Virginia, alleged Indivior made billions of dollars by deceiving doctors and health care benefit programs into believing the film version of its Suboxone treatment was safer and less susceptible to abuse than similar drugs.

Shares in the company crashed as much as 80%, wiping out 620 million pounds ($811.73 million) in market value, and touching their lowest since listing in 2014.

Shares in Reckitt Benckiser, from which Indivior was spun out, slumped 5% to the bottom of London's blue chip FTSE 100 index, erasing many of the gains made in 2019 after three tough years.

Reckitt wasn't charged but the indictment said the illegal marketing began before the spin-off.

"This indictment is not against RB Group Plc or any other group company and we currently have no additional or new information in respect of this matter, apart from what has been publicly issued by the Department of Justice and Indivior Plc," Reckitt responded in a brief statement on Wednesday.

It referred investors back to a previous statement that it was recognizing a provision of $400 million relating to the issue, but that its final cost could be substantially higher.

Tough times

Indivior had prospered as U.S. officials stepped up efforts to combat an opioid epidemic that President Donald Trump has declared a public health emergency. U.S. sales account for 80% of last year's $1 billion in revenue.

Shares, however, had already been hurt by expectations of a slump in Suboxone sales with the arrival of new generic competition this year and the company has struggled to convince analysts and financial investors that it has an adequate replacement.

The company is scheduled to be arraigned in court on May 6 and plans to plead not guilty at that hearing, according to a spokesman.

This also comes at a bad time for Reckitt, which was just starting to regain investor confidence after a series of one-off problems including a safety scandal in South Korea, a failed product launch, a cyber attack and a manufacturing glitch.

Its chief executive Rakesh Kapoor, who oversaw several acquisitions and divestitures with the aim of turning Reckitt into a global consumer health care company, will retire this year, even though a major undertaking, splitting Reckitt into two business units, is unfinished.

Potential punishment

In an indictment that charged Indivior and its subsidiary Indivior Inc with conspiracy, health care fraud, mail fraud and wire fraud, the government said it would seek to have it forfeit at least $3 billion.

"An adverse verdict may have a material adverse effect on the company and its financial position and outlook," Indivior said.

The potential penalty is triple last year's annual revenue. The company had net cash of $681 million at the end of the year.

Indivior said in a statement it was "extremely disappointed" by the department's decision to charge it, and added it would vigorously contest it.

"The headline potential penalties are severe but a settlement is also still possible," Jefferies analysts said in a note.

Indivior has spent the last two years fighting multiple legal battles and patent disputes in the United States with companies including Dr. Reddy's Laboratories Ltd., Teva Pharmaceuticals Industries Ltd. and Mylan Pharmaceuticals Inc. to block them from launching generics.

Reckitt fears

Reckitt spun off its pharmaceuticals business into Indivior in 2014, as the shrinking unit battled competition from cheaper generic rivals.

The spin-off, and the 2017 sale of Reckitt's food unit, let Reckitt focus on expanding its consumer health business, which targets aging populations and those interested in health and wellness in the West and rising incomes in developing markets.

In addition to concern about Reckitt's direct liability from the charges, investors on Wednesday worried about a possible spillover effect on Reckitt's infant formula business.

The company had previously flagged implications including "potential criminal indictment of the group or employees, with reputational impact, distraction and potential debarment which could theoretically extend" to its infant formula business.

The business, which sells Enfamil formula, derives a portion of its sales from government contracts in the U.S. supplying a program to support low-income parents.

However, Reckitt said on Wednesday any risk to the infant formula business was theoretical and seen as "highly unlikely and only a remote possibility."