A UK-based drugmaker has agreed to pay a record $1.4 billion settlement to the US government in order to end criminal and civil probes into allegations of illegal marketing of opioid addiction treatment medication, according to the Justice Department.

The settlement with Reckitt Benckiser Group (RB Group) will include multiple investigations into a subsidiary, Indivior (formerly Reckitt Benckiser Pharmaceuticals Inc.).

"Opioid withdrawal is difficult, painful, and sometimes dangerous; people struggling to overcome addiction face challenges that can often seem insurmountable," said assistant Attorney General Jody Hunt of the DOJ's Civil Division. "Drug manufacturers marketing products to help opioid addicts are expected to do so honestly and responsibly."

Suboxone, which proved to be a blockbuster-selling drug for Indivior, is an addiction-fighting medication that also contains opioids. Indivior was spun off into a separate company from the RB Group in December 2014, but the exposure and looming litigation and probes related to Suboxone were still attached to the parent company.

On April 9, a federal grand jury in Virginia indicted Indivior for "allegedly engaging in an illicit nationwide scheme to increase prescriptions of Suboxone," according to the DOJ. The company denied the charges and trial is scheduled to start in May 2020.

Federal prosecutors charged that Indivior allegedly marketed a version of Suboxone (Suboxone Film) to medical professionals as less addictive and safer than other drugs containing its active ingredient, the opioid buprenorphine, according to the DOJ statement. -ABC News

According to the indictment, Indivior's "Here to Help" web and phone resources actually funneled opioid-addicted patients to doctors who were actively prescribing Suboxone and other opioids "to more patients than allowed by federal law, at high doses, and in a careless and clinically unwarranted manner."

The company was also accused of discontinuing its tablet form of Suboxone "based on supposed 'concerns regarding pediatric exposure' to tablets, despite Indivior executives’ knowledge that the primary reason for the discontinuance was to delay the Food and Drug Administration’s approval of generic tablet forms of the drug."

Included in the settlement is an immunity agreement, while RB Group will forfeit $647 million of proceeds from the sale of Indivior - nor will it manufacture, market or sell Schedule 1 - 3 controlled substances for three years.

That said, it's not over for Invidior.

The trial against the RB Group's former subsidiary Invidior is still slated to start next May. Thursday's settlement was only with RB Group, and not Indivior.

In addition, the company also agreed to pay $700 million in civil settlements to the federal government and six states, as well as $50 million to the Federal Trade Commission.

RB issued a statement denying any wrongdoing.

"While RB acted lawfully at all times and expressly denies all allegations that it has engaged in any wrongful conduct, after careful consideration, the board of RB determined that the agreement is in the best interests of the company and its shareholders," they said.