May 6 (Reuters) - Massachusetts sued a unit of French advertising company Publicis Groupe SA on Thursday, accusing it of fueling the U.S. opioid epidemic by using unfair and deceptive marketing to help the drugmaker Purdue Pharma sell more OxyContin. The state’s attorney general, Maura Healey, accused Publicis Health of working with drugmakers from 2010 to 2019 on campaigns to persuade doctors to prescribe more opioids for longer periods of time, including to patients who did not need them. She said Publicis collected more than $50 million from Purdue alone, including for efforts to “humanize” opioids and make doctors prescribe them to a wider pool of patients. Publicis Health did not immediately respond to a request for comment. The lawsuit filed in a state court in Boston seeks civil penalties, restitution to victims and a declaration that the unit created a public nuisance. Healey’s lawsuit followed agreements this year by the consulting firm McKinsey & Co to pay $641 million to resolve lawsuits by all 50 U.S. states, Washington, D.C., and five U.S. territories over its role in the epidemic. The U.S. Centers for Disease Control and Prevention has said nearly 500,000 people died from opioid overdoses from 1999 to 2019. Purdue is operating in bankruptcy. In March, it proposed a restructuring plan that would steer profits to opioid victims and require members of the Sackler family who own the company to contribute nearly $4.3 billion. (Reporting by Jonathan Stempel in New York; Editing by Dan Grebler) Our Standards: The Thomson Reuters Trust Principles.