US drugmakers and distributors go on trial in Central Islip, New York before a jury for the first time accused of stoking an opioid addiction epidemic that has left more than half a million Americans dead from overdoses.

US pharmaceutical firms accused of stoking a two-decade epidemic of opioid addiction that has seen 500,000 die from overdoses stood trial before a jury for the first time Tuesday.

The suit launched by two counties in New York state charges the leading drugmakers and distributors with earning huge profits by pushing highly addictive prescription opioids like Oxycontin that cost local authorities billions of dollars for social services in dealing with the fallout from the epidemic.

"This case is about one thing: corporate greed," the suit says.

The drug makers and distributors "put their desire for profits above the health and wellbeing" of the citizens of the counties, the suit said.

On trial are firms including Actavis, Cardinal Health and Amerisource, dominant powers in the US healthcare industry.

The initial complaint also included Purdue Pharma, whose involvement in the case has been paused due to bankruptcy, and Johnson & Johnson, which is no longer part of the lawsuit after announcing a settlement over the weekend, among others.

Civil and criminal charges have been launched in front of judges around the country against the firms, with some of those cases resulting in negotiated settlements for heavy damages.

The case that opened in Central Islip, New York Tuesday will be the first in which the companies will be judged by a jury of citizens, who could, if convinced of their guilt, award the counties massive damages that could create a framework for similar suits and jury trials all around the country.

"The evidence is going to show that the manufacturing defendants misled doctors and patients by claiming that the risk of addiction was rare," said Jayne Conroy, who represents the Long Island county of Suffolk, one of the two counties named as plaintiffs in the suit.

"The opioid epidemic didn't happen by accident. It happened because of a calculated decision in boardrooms across the country to decide to try to make a blockbuster drug... that everyone knew was addictive, and cause death," said Hunter Shkolnik, representing Nassau County.

On the eve of the trial four major pharmacy chains including CVS and Walgreens were dropped from the list of defendants because they had reached settlements with the state, according to news reports.

The trial is taking place in a university auditorium because the courtroom is not large enough to contain all of the defendants and their attorneys.

It is expected to last six to eight weeks.