"Based on this evidence, a jury could reasonably conclude that the increases in prescription opioids proximately caused harm to plaintiffs," wrote Polster in his order denying motions for summary judgment on causation, a key defense for the opioid companies. "Because plaintiffs have presented evidence that shows they have suffered the sort of injury that would be an expected consequence of the alleged wrongful conduct, plaintiffs have made a sufficient showing to withstand summary judgment on this issue."

He also denied motions for summary judgment on federal preemption, another defense, and refused to toss civil conspiracy claims. Other claims over which he has yet to rule include public nuisance and violations of the U.S. Racketeer Influenced and Corrupt Organizations, or RICO.

Lead plaintiffs counsel Paul Farrell of Greene, Ketchum, Farrell, Bailey & Tweel; Paul Hanly of Simmons Hanly Conroy; and Paul Hanly of Simmons Hanly Conroysaid in an emailed statement: "We are pleased that Judge Polster's reasoned opinions have almost uniformly agreed with plaintiffs' positions on the appropriate legal standards to be applied in these cases and that the court has denied nearly all of defendants' motions for summary judgment and for exclusion of testimony."

Most of the defendants did not respond to requests for comment. Representatives from Purdue and McKesson declined to comment, as did Brien O'Connor of Ropes & Gray, who represents another manufacturer, Mallinckrodt Pharmaceuticals.

Sabrina Strong of O'Melveny & Myers speaking for Johnson & Johnson and its subsidiary, Janssen Pharmaceuticals, wrote in a statement, "Janssen's medicines play a unique role in the lives of those who need them, and the company responsibly marketed Duragesic, Nucynta and Nucynta ER, which since launch have accounted for less than 1% of total opioid prescriptions in the United States. Preparations continue for upcoming proceedings in the MDL."

The rulings come after the first trial in the nation over the opioid crisis ended last week with a $572 million judgment against Johnson & Johnson. That trial, in a case brought by Oklahoma Attorney General Mike Hunter, was before a judge and involved a single claim of public nuisance.

Another attorney general, Dave Yost, who has brought two cases on behalf of the state of Ohio over the opioid crisis, petitioned the U.S. Court of Appeals for the Sixth Circuit on Friday to halt next month's trial in Cleveland. He raised concerns that a potential settlement or verdict for the Ohio counties would lead to misallocation of funds and hamper the state's case.

In the federal trial in multidistrict litigation, Polster refused to dismiss claims last year.

In Polster's causation order, which affects all the claims, the manufacturers had argued that their alleged fraudulent marketing of the drugs did not result in increased opioid prescriptions, but plaintiffs countered with evidence of a substantial increase in the supply.

"Construing this evidence in the light most favorable to plaintiffs, a factfinder could easily conclude the manufacturer's misleading marketing activities resulted in a substantial increase in the supply of prescription opioids," Polster wrote.

As to the distributors, the distributors and pharmacies had argued that the acts of others, such as criminals involved in opiate narcotics and doctors making illegal prescriptions, harmed the Ohio counties—not their alleged failures to report suspicious orders under the federal Controlled Substances Act.

Polster, however, wrote that a jury could find that "massive increases" in prescription opioids in both counties, and evidence of "a complete failure by the distributors and pharmacies to maintain effective controls against diversion" could be a "substantial factor in producing the alleged harm suffered by plaintiffs."

In his preemption order, Polster relied on his previous decisions in refusing to grant motions by four separate groups of defendants, including manufacturers, distributors and pharmacies.

"The court has previously rejected manufacturers' narrow construction of plaintiffs' allegations as effectively demanding nothing more than label changes, and does so again," he wrote.

Addressing another judge's summary judgment decision that tossed the state of North Dakota's entire opioid case against Purdue, Polster found the May 10 ruling to be, "by leaps and bounds, an outlier on the question of preemption." In a footnote, he cited contrary preemption holdings by judges in cases brought by the state of Ohio, New Jersey, New Hampshire and Washington.

On the civil conspiracy claim, Polster found that plaintiffs' evidence of coordinated marketing strategies, timing of opioid orders and involvement in trade organizations should go before a jury.

"The court cannot conclude that no reasonable jury could find for plaintiffs on the question of whether the manufacturer defendants entered into a conspiratorial agreement or malicious combination," he wrote. As to the distributors, he wrote, "A reasonable jury could review the record evidence and find that distributor defendants shared a general conspiratorial objective, with themselves and with other defendants, to expand the opioid market and disregard regulatory obligations in order to achieve that goal."

Read more: 

• Lawyers in opioid suit seek nationwide class certification
• New lawsuit unveils scope of Purdue's 'extraordinary efforts' to push opioids
• Opioid manufacturers: A public nuisance?