Indivior PLC (LON:INDV) said former parent Reckitt Benckiser PLC (LON:RB.) has filed a claim for more than £1bn under an indemnity signed in 2014 when the two demerged.
The amount in the writ is a little over £1.073bn and Invidior said it will assess its merits with advisors though it added that as yet the claim had not been served on the company.
Indivior has been dogged by lawsuits over its opioid dependency treatment Suboxone ever since the demerger.
The group has been fighting off generic competitors claiming its patent has run out, while also battling multiple legal actions over how the drug was marketed.
In October, former chief executive Shaun Thaxter was sentenced to six months in prison and ordered to pay US$0.6mln in fines.
Thaxter “failed to prevent efforts to build profits through misleading safety claims, which led to millions of dollars in ill-gotten gains for Indivior”, the US Attorney Daniel P Bubar said.
Indivior had earlier agreed to pay US$600mln to the US Department of Justice, the Federal Trade Commission (FTC) and various state attorneys general as part of a settlement over the way Suboxone was marketed.
A year earlier Reckitt Benckiser agreed to pay around US$1.4bn to the US authorities in an effort to draw a line under the issue.
That settlement related to a Department of Justice investigation which accused Indivior of illegally boosting prescriptions of Suboxone.
An indictment claimed Indivior had marketed its star drug as safer and less abusable than other treatments, deceiving healthcare providers and allowing the company to rake in billions of dollars in extra sales.
It was also accused of pushing patients towards doctors who it knew were prescribing opioids “at high rates and in a clinically unwarranted manner”.
Reckitt denied the allegations but said it had settled the claims to avoid further litigation and uncertainty.
Shares in Indivor tumbled 40% to 75.7p valuing the group at £560mln. Reckitt dropped 1% to 6,520p.
