America's three largest pharmacies have been found liable for spurring on a painkiller crisis in two Ohio counties, in a landmark case.

A US federal court found that Walgreens Boots Alliance, CVS, and Walmart, by their policies, created an oversupply of addictive opioid pills.

Lawyers for the two Ohio counties, Lake and Trumbull, said the costs are potentially $1 billion for each county, to cover social and legal expenses related to the impact of the opioid epidemic.

"The judgement today against Walmart, Walgreens and CVS represents the overdue reckoning for their complicity in creating a public nuisance," the lawyers said, in a joint statement.

Public nuisance

The pharmacies “created a public nuisance by failing to ensure opioid prescriptions were valid,allowing excessive quantities of addictive pain-pills to flood their communities,” the lawyers said.

Walgreens Boots Alliance, CVS and Walmart denied the allegations, saying they had taken steps to prevent painkillers being diverted from their intended legal use.

CVS is to appeal the judgment. There was no immediate comment from the other retailers.

"As plaintiffs' own experts testified, many factors have contributed to the opioid-abuse issue, and solving this problem will require involvement from all stakeholders in our healthcare system and all members of our community," CVS said.

Other US cases will use the "public nuisance" line to target the companies involved in making and distributing the opioid painkillers, although courts in Oklahoma and California have turned it down as a legal argument.

The compensation due to the two Ohio counties will be decided at a later hearing.

Over-prescription of FDA-approved legal opiates, such as Oxycontin and Fentanyl, have caused millions of Americans to slide into addiction over the past 20 years.

500,000 deaths

An estimated 500,000 deaths have been caused by opiate overdoses between 1999 and 2019.

The painkiller epidemic drained the resources of State and local governments, and some 3,300 cases are pending in an attempt to recoup funds from massively profitable firms that sold the painkillers over the counter.

Pharmaceutical companies and medical professionals have also been accused of accelerating the opioid crisis.