CLEVELAND, Nov 15 (Reuters) - Lawyers for pharmacy chains including CVS and Walgreens on Monday argued they were not to blame for the U.S. opioid epidemic, as jurors prepared to consider whether to hold them responsible for the devastation the drug crisis caused in two Ohio counties. Mark Lanier, a lawyer for Lake and Trumbull counties, told a federal jury in Cleveland that a verdict in the case against CVS Health Corp (CVS.N), Walgreens Boots Alliance Inc (WBA.O) and Walmart Inc (WMT.N) would have ramifications across the country. The trial is the first the pharmacy chains have faced in thousands of lawsuits by states and local governments seeking to hold them liable for an epidemic that U.S. health officials say has led to nearly 500,000 opioid overdose deaths over two decades. "You get to decide what will be the most seminal case in pharmacy history," Lanier said in his closing argument.He argued that companies created a public nuisance in the form of the epidemic by failing to prevent excessive amounts of addictive pain pills from flooding the counties or by stopping bogus prescriptions from being filled. "A pharmacy is not a gum ball machine," Lanier said. "They have more responsibility than simply taking your money and getting you your pills." Defense lawyers countered that the companies took steps to guard against the diversion of pills and blamed others for the deadly epidemic. "There are many, many actors who played a role in the opioid crisis: The manufacturers, government agencies, doctors, drug cartels," CVS attorney Eric Delinsky said. Brian Swanson, a lawyer for Walgreens, said it had policies in place since 1997 to identify "red flags" of misuse and kept improving them. "A company that"s constantly updating and improving its policies is not a company acting intentionally to cause an opioid crisis," he told jurors. LAWSUITS FILED NATIONWIDE Should the jurors find the pharmacies created a public nuisance, U.S. District Judge Dan Polster would decide how much they owe to abate, or address, it. The counties" lawyers have said the costs are potentially $1 billion for each county. The Ohio trial follows recent setbacks for plaintiffs pursuing some of the 3,300 opioid cases filed against drug manufacturers, distributors and pharmacies. Oklahoma"s top court last Tuesday overturned a $465 million judgment against drugmaker Johnson & Johnson, and a California judge this month ruled in favor of four drugmakers in a case brought by several large counties. Those lawsuits also accused the companies of creating a public nuisance. A similar lawsuit by Washington state against three drug distributors went to trial on Monday. read more