The only manufacturer is Teva.

Last year, these five companies had combined total revenues of more than half a trillion dollars.

What will the plaintiffs try to prove?

Seeking $8 billion, the plaintiffs claim the distributors conspired to flout the federal law that requires them to monitor sales and report outliers. They say they will argue that the distributors lobbied members of Congress for favorable legislation and not only cast a blind eye on supersize orders but rewarded sales teams that brought them in.

They also intend to show the devastation that unfolded from the yearslong pill dump: how addiction ate into every sector of county life, crippling budgets for law enforcement, foster care and first-responder squads. Expect testimony from addiction medicine specialists as well as testimony from people who have struggled with opioids.

What will the defendants argue?

Causation is a critical question. The distributors are expected to say they were simply delivering medication made by the drug manufacturers, approved by the government and prescribed by doctors. Their defense may include a recent report from a federal watchdog that accuses the Drug Enforcement Administration of lax oversight of opioids.

The defense also intends to describe a shifting medical culture: In the late ’90s, when OxyContin first appeared, prescribers were urged to focus on undertreated pain with new, supposedly nonaddictive drugs. The prescribing of opioids changed — from using them for end-stage cancer to making them the go-to drug for acute and chronic pain.

In the courtroom

For the plaintiffs: Mark Lanier, long recognized as one of the country’s best tort trial lawyers. With his native Texas drawl, the boyish energy of a man who built and runs a train on his 40-acre estate, and a preacher’s conviction, Mr. Lanier has exacted giant-killer jury verdicts from Johnson & Johnson and Merck. On Sunday, Mr. Lanier turned 59 and, as he usually does when working out of town, flew back to Houston on his private plane to deliver his Sunday Bible study lecture, typically attended by hundreds. His firm has just taken on Juul, on behalf of a New Jersey teenager.