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A bipartisan group of attorneys general from across the country are investigating the role that pharmaceutical companies played in creating and prolonging the opioid epidemic. The probe, which is led by AG offices in Washington D.C. and Tennessee and includes the majority of states, will focus on whether the marketing and sale of prescription painkillers was unlawful.

“Our ongoing investigation is going straight into the boardrooms of pharmaceutical companies.”

“The people peddling the drugs ripping apart our towns aren’t only on our street corners,” said Pennsylvania AG Josh Shapiro in a prepared statement. “Three out of four heroin users started by abusing prescription opioids, and our ongoing investigation is going straight into the boardrooms of pharmaceutical companies.”

The AGs have yet to release details on the companies being investigated and how far along in the investigation they are, but say they are “using subpoenas for documents and testimony” to determine next steps. According to a Wall Street Journal article about the investigation, “The multi-state effort is months in the making, according to people familiar with the matter, and subpoenas have already been issued against some targets. The probe is in the investigatory stage and could lead to litigation, though such investigations can be protracted and don’t necessarily lead to lawsuits in every instance.”

Overdoses deaths have reached an all-time high, killing more Americans than guns or cars. Public health experts have long blamed today’s widespread addiction to opioids—including painkillers, heroin, and fentanyl—on overzealous marketing and liberal prescribing of opioid painkillers, starting with the introduction of OxyContin in the mid-90s. (For more background, check out our opioid explainer.)

Following the Journal article, a number of states announced their involvement on Thursday. So far, Washington D.C., Pennsylvania, Massachusetts, Vermont, Illinois, Texas, Georgia, Connecticut, South Dakota, Rhode Island, Alabama, Virginia, Wisconsin, Tennessee, Colorado, Indiana, Delaware, Iowa, North Carolina, Oklahoma, New York, and California have announced their participation publicly. Some states AG offices declined to comment due to state laws prohibiting discussing ongoing investigations.

This is far from the first probe into opioid makers’ deceptive marketing. Last month, Ohio sued five pharmaceutical companies,—including Purdue Pharma (maker of OxyContin), Endo Health Services (Percoset, Opana), and Johnson & Johnson (Duragesic)—accusing them of misleading doctors and patients about the dangers of painkiller addiction. Last week, Nassau County, New York, sued drugmakers, distributors, and doctors, saying it had to spend more on health care and law enforcement as a result of the crisis. As a recent Bloomberg article noted, over the past year alone, more than 20 US states, counties, and cities have sued opioid manufacturers claiming that their deceptive marketing contributed to today’s public health crisis.

Asked about the allegations in the Ohio case, Purdue Pharma released a statement saying company officials are concerned about the opioid epidemic and “committed to working collaboratively to find solutions.” Endo Health Services declined to respond. Janssen, the J&J branch selling opioids, said the company acted “appropriately, responsibly, and in the best interest of patients.”