(Adds comments from drug companies, details on New Hampshire Supreme Court decision)
By Heide Brandes and Nate Raymond
OKLAHOMA CITY/BOSTON, June 30 (Reuters) - Oklahoma on Friday joined growing litigation over claims drugmakers misrepresented the risks of opioid painkillers, as New Hampshire cleared a hurdle in its own probe of the role played by companies in the national addiction epidemic.
Oklahoma Attorney General Mike Hunter filed a lawsuit in Cleveland County District Court against Purdue Pharma LP, Johnson & Johnson, Allergan Plc and units of Teva Pharmaceutical Industries Ltd.
The drugmakers engaged in a "fraudulent, decades-long marketing campaign to profit from the suffering of thousands of Oklahomans," Hunter said.
"The lawsuit claims the companies knowingly marketed their drugs as safe for chronic pain management while downplaying the risk of opioid dependency," he added.
Purdue, which makes OxyContin, said it denies the allegations but shares Hunter's concerns about the epidemic.
J&J said it acted appropriately, adding that its opioid medications carry U.S. Food and Drug Administration-mandated warnings about their risks.
Allergan said it supports the safe, responsible use of prescription medications. Teva said it is committed to the appropriate promotion and use of opioids.
Opioids, including prescription painkillers and heroin, killed more than 33,000 people in the United States in 2015, according to the U.S. Centers for Disease Control and Prevention.
Oklahoma's lawsuit followed similar cases brought against some of the same companies by Mississippi, Ohio and Missouri. Several cities and counties in California, Illinois, Ohio, Tennessee and New York have also filed lawsuits over companies' marketing of opioids.
A group of state attorneys general announced an investigation this month of the role played by pharmaceutical companies in the opioid epidemic.
The states investigating include New Hamsphire, where the highest state court on Friday overturned a lower-court ruling that prevented the enforcement of subpoenas against five drugmakers.
The lower-court's decision was based on a finding, now reversed, that the attorney general acted outside his authority by executing a contingency fee agreement with a private law firm to pursue the case.
"This case is massive in scope, and we do not have sufficient resources without assistance of outside counsel," said James Boffetti, chief of the New Hampshire attorney general's consumer protection bureau.
Boffetti said Purdue is the probe's current focus. The state had been working with Cohen Milstein Sellers & Toll to push its investigation forward but it is now relying on Motley Rice after the case's lead attorney switched firms.
Purdue said it was disappointed and believes "that privatizing law enforcement presents serious public policy concerns." (Writing by Nate Raymond in Boston; editing by Tom Brown)