The Justice Department is investigating McKinsey & Company, the international consulting giant, for its role in helping drug companies maximize their sale of opioids.

The investigation is led by the U.S. attorneys’ offices in Massachusetts and the Western District of Virginia in coordination with the department’s civil division in Washington, according to two officials familiar with the case who spoke on condition of anonymity.

Since 2021, McKinsey has agreed to pay about $1 billion to settle investigations and lawsuits across the United States related to the firm’s work with opioid makers, principally Purdue Pharma, the maker of OxyContin. McKinsey recommended that Purdue “turbocharge” its sales of the drug in the midst of the opioid crisis, which has killed hundreds of thousands of Americans. McKinsey has not admitted any wrongdoing.

News of the criminal investigation was first reported by The Wall Street Journal on Wednesday.

The investigation has been underway for several years. Endo, a pharmaceutical company that hired McKinsey to advise on the sale of the opioid Opana, said in a regulatory filing that it received a subpoena in December 2020 from the Western District of Virginia seeking information about McKinsey. The New York Times reported on the existence of that subpoena in 2022. Last year another opioid maker, Mallinckrodt, said it received a grand jury subpoena from the same U.S. attorney’s office but did not mention any connection to McKinsey.

Federal prosecutors are also looking into whether McKinsey obstructed justice in its handling of records, according to The Journal.

By 2018, senior McKinsey consultants were growing increasingly worried that they might be held to account for their opioid work. On July 4 of that year, Martin Elling, a leader in the firm’s pharmaceutical practice, made a decision he would later regret. He sent an email to Arnab Ghatak, a senior partner, asking whether they should eliminate documents and emails connected to opioids.

Mr. Ghatak replied: “Thanks for the heads up. Will do.”

Both men were fired after The Times reported in 2020 about the existence of the emails.

It isn’t unusual for criminal investigations like this to go on for many years, especially ones involving two U.S. attorneys’ offices, the Justice Department and possibly state agencies as well, Rick Mountcastle, a former federal prosecutor, said.

He led a criminal investigation into Purdue Pharma that resulted in the company’s guilty plea in 2007 to having misled regulators, doctors and patients about the dangers of OxyContin. “It is a huge monster bureaucracy that moves at a very slow pace,” said Mr. Mountcastle, who was not a source confirming the existence of the investigation.

McKinsey made about $86 million over many years advising Purdue Pharma. The bulk of that work took place after Purdue’s guilty plea. In 2019, McKinsey said it would no longer advise clients on opioid-related business.

Ramiro Prudencio, a spokesman for McKinsey, declined to comment. A spokesman for the Justice Department had no comment on the case.