The race for New Jersey governor has taken a sharp, unexpected turn less than a month before Election Day with the opioid crisis taking center stage amid explosive charges by the Democratic nominee, Representative Mikie Sherrill.

The latest twist in the race came on Monday when Ms. Sherrill, joined by a substance abuse counselor and a man whose brother overdosed on prescription painkillers, again blamed her Republican opponent, Jack Ciattarelli, for spreading misinformation about opioids.

Her words were far more nuanced than the stunning assertion she made last week during a debate in which she accused Mr. Ciattarelli of being responsible for the deaths of “tens of thousands of people.”

But her central claim was unchanged: that a medical publication company that Mr. Ciattarelli owned until 2017 had made it easier for people to get prescription opioids.

During Wednesday’s debate, Ms. Sherrill said: “You killed tens of thousands of people by printing your misinformation, your propaganda and then getting paid to develop an app so that people could more easily get the opioids once they were addicted.”

“You then went on to kill tens of thousands of people in New Jersey, including children,” she added.

“It’s a lie,” Mr. Ciattarelli replied. “I’m proud of my career.”

Mr. Ciattarelli’s campaign has flatly denied the charge and said it planned to file a defamation lawsuit against Ms. Sherrill this week. “Baselessly and recklessly accusing a political opponent of mass murder in a televised debate crosses the line,” Chris Russell, Mr. Ciattarelli’s chief strategist, said. (The campaign has twice before threatened to sue over unrelated issues, but has yet to follow through.)

But Ms. Sherrill’s rhetoric has nonetheless inserted a volatile new element into a race that has drawn an extraordinary amount of money and interest from national Democratic and Republican Party leaders, who are hoping to demonstrate strength in New Jersey on Nov. 4. The contest — one of just two governor’s races this year — is considered an early test of voter attitudes toward President Trump ahead of the 2026 congressional races.

Both candidates have intensified their negative attacks in recent weeks, and each has accused the other of selectively splicing video footage to create misleading ads.

According to most polls, Ms. Sherrill, a former Navy helicopter pilot, is the front-runner. But her abrupt departure from an otherwise carefully curated campaign message has left Republicans suggesting that the race is far closer than surveys suggest.

It has also brought renewed attention to Mr. Ciattarelli’s career as a publisher in the medical field whose company, Galen Publishing, produced material for universities and other clients, often with money supplied by pharmaceutical companies.

Here’s what we know about Ms. Sherrill’s claims, Mr. Ciattarelli’s business and an online tool his company helped to create that was known as “Living With Pain.”

Opioid Deaths in New Jersey

Opioid overdose deaths in New Jersey, and nationwide, surged between 2012 and 2018. During those years, 11,107 New Jersey residents died from overdoses of prescription and illicitly produced opioids, including heroin, according to state Health Department data.

When asked about Ms. Sherrill’s claim that Mr. Ciattarelli had “killed tens of thousands” of residents, her spokesman cited the additional 12,837 opioid deaths in New Jersey since 2018, after Mr. Ciattarelli sold his company.

Galen Publishing was a medical education company focused on producing journals and developing content for continuing education programs in association with universities. It did not manufacture opioids.

Living With Pain was not an app, but a collection of interactive online video modules. It is now defunct, and The New York Times was unable to independently verify its contents or view any of the roughly 70 to 100 videos that were set to be included on the website. The Ciattarelli campaign said it did not have the videos, noting that Mr. Ciattarelli had not owned the company for eight years. They do not turn up in a search of the internet.

The site was created to “help patients start the conversation with their doctor and take control of their pain,” according to an email from a manager at Teva Pharmaceuticals, a company that manufactured generic opioids and funded the online tool. Mr. Russell, Mr. Ciattarelli’s strategist, said that Mr. Ciattarelli’s company had “helped to create an online tool aimed at helping chronic pain sufferers educate themselves on treatment options.”

“Mikie Sherrill can’t provide any evidence of her reckless claim that Jack’s publishing company pushed people toward opioids because it never, ever happened,” Mr. Russell said on Monday.

‘Living With Pain’

Advanced Studies in Medicine, a component of Mr. Ciattarelli’s company, Galen Publishing, received $139,800 in funding from Teva Pharmaceuticals to work on what became known as Living With Pain, according to internal corporate documents compiled by the University of California, San Francisco, and Johns Hopkins University. (The repository of records offers a searchable database of documents from pharmaceutical companies that were turned over in opioid lawsuits.)

Living With Pain started in August 2016 and was designed to help patients with chronic pain “take a more active role in symptom and medicine identification/treatment,” according to an internal PowerPoint presentation provided during litigation over claims that Teva contributed to the opioid crisis. A payment spreadsheet submitted in connection with a lawsuit noted that the program was supposed to end in June 2018.

Advanced Studies in Medicine helped develop the online tool in collaboration with another company, ProPatient, and with the U.S. Pain Foundation, a nonprofit advocacy organization helping people with conditions causing chronic pain, according to the PowerPoint presentation. The U.S. Pain Foundation has accepted millions of dollars from pharmaceutical companies.

According to the email from the Teva manager, Mr. Ciattarelli’s company was expected to introduce the Living With Pain interactive tool to health care providers, who would be “encouraged to provide their patients with access” to the site.

It was ProPatient that operated a companion mobile app that allowed patients to download checklists and customize “questions for doctor,” according to the presentation.

Living With Pain was released just as the federal government was taking new steps to try to reduce opioid prescriptions, amid rising overdoses and deaths. In 2016, following months of arguments with drug industry groups, the Centers for Disease Control and Prevention released guidelines urging doctors to first recommend pain relievers such as ibuprofen before prescribing opioids. In turn, some patients with chronic pain had a harder time obtaining the medicines that eased their suffering.

Pharmaceutical companies have since paid billions of dollars in jury verdicts and to settle lawsuits seeking to hold them responsible for the deadly opioid epidemic. Teva settled in 2022 with states and local governments in a deal worth up to $4.25 billion.

In 2016, Teva anticipated that perhaps 15,000 patients might use Living With Pain as a resource, according to the internal email.

But when it was released, the online tool was hardly a runaway hit. In the two weeks after it was introduced, only 34 people had created an account and there were 143 guest users, according to the PowerPoint presentation turned over in litigation against Teva.

Officials with Teva and ProPatient did not respond to requests for comment.

The chief executive of the U.S. Pain Foundation, Nicole Hemmenway, said in an email that her organization did not have a relationship with any of the groups involved in the Living With Pain project and did not have access to the videos.

Ciattarelli’s Company

Galen Publishing produced journals bearing the name of Johns Hopkins University, among other universities.

It held a long-running contract with the University of Tennessee Health Science Center and its College of Pharmacy. There were webcasts, symposia and an academic journal, according to a letter by a University of Tennessee official. As was common for medical education companies, funding — more than $13 million over nearly a decade — came from pharmaceutical giants: Bristol Myers Squibb, Pfizer, Purdue Pharma, Teva, Gilead Sciences and Merck, among others.

Mr. Ciattarelli, a former state assemblyman, sold Galen Publishing in 2017, netting him millions and giving him time to focus on running for governor; this is his third race for the office.

Dr. G. Caleb Alexander, a professor of medicine and epidemiology at the Johns Hopkins Bloomberg School of Public Health, helps to manage the archive of opioid litigation documents and testified as an expert witness for government entities that sued in connection with the opioid crisis.

Dr. Alexander said he was not familiar with the specifics of Ms. Sherrill’s claims or Mr. Ciattarelli’s business. But he said that, in general, medical education companies “grossly overstated the benefits of opioids and understated their risks.”

“Were they on the wrong side of the epidemic? I think most people would say, ‘yes,’ ” Dr. Alexander said.

But he said that it would be wrong to attribute a certain number of deaths to any individual medical education company.

“It’s just a complex and fraught undertaking to attribute a certain amount of harm to this or any other communications company,” he said.