The McKesson Corp. headquarters in San Francisco. (PAUL SAKUMA/ASSOCIATED PRESS)

Two of the nation’s biggest drug distributors shipped 12.3 million doses of powerful opioids to a single pharmacy in a tiny West Virginia town over an eight-year period, a congressional committee revealed Thursday.

The Family Discount Pharmacy in Mount Gay-Shamrock received the drugs from McKesson Corp. and Cardinal Health between 2006 and 2014, according to the House Energy and Commerce Committee.

The committee is investigating the sale of pills in West Virginia by wholesale drug distributors, which are required by law to monitor and report to the Drug Enforcement Administration suspicious purchase orders for opioids. When they do not, millions of pills can be diverted to users and dealers from a single pharmacy.

The new data is included in letters sent by the committee Thursday to the “Big Three” drug distributors — McKesson, Cardinal and AmerisourceBergen — demanding more information on the steps they took during those years to keep drugs off the black market.

The committee said it had analyzed data provided by the DEA to determine that Cardinal Health sent Family Discount more than 6.5 million hydrocodone and oxycodone pills between 2008 and 2012. It said McKesson sent the pharmacy 5.8 million pills between 2006 and 2014. Smaller distributors also sold narcotics to the drugstore — in a rural town with 1,779 residents in 2010 — bringing the total to nearly 16.6 million by 2016.

McKesson is the fifth-largest company in the United States, with revenue of more than $192 billion, according to the Fortune 500 list. Cardinal ranked 15th on the list, with $121 billion in revenue.

West Virginia has by far the highest rate of drug overdose deaths in the United States, at 52 people per 100,000 in 2016.

“We need detailed answers and documents from these national distributors as to why large volumes of opioids were distributed to certain areas of the state,” the committee’s chairman, Rep. Greg Walden (R-Ore.), and ranking Democrat, Rep. Frank Pallone Jr. (D-N.J.) said in a statement. “West Virginians and families devastated by the opioid crisis all over the country deserve answers.”

On Jan. 26, in letters to two smaller distributors, the committee cited data showing that wholesalers collectively sent 20.8 million doses of the painkillers to two pharmacies four blocks apart in Williamson, W.Va., a town of 2,900 people.

Cardinal Health said in an email that “we can confirm that we received a letter from the House Energy & Commerce Committee, and we look forward to cooperating with them in the future.” AmerisourceBergen spokesman Gabe Weissman said in a statement that the company anticipates an “ongoing conversation with the committee while continuing our work with regulators, enforcement agencies and other participants in the health care system to do our part in combating prescription drug abuse.”

McKesson Corp. did not reply to a request for comment.

In a separate report this week, Sen. Claire McCaskill (D-Mo.) showed that five drug manufacturers paid more than $10 million to patient advocacy groups and doctors who promoted painkillers, potentially exacerbating the nation’s opioid crisis.

The report shows how the pharmaceutical industry funneled money to organizations that, in some cases, downplayed the risks of opioid use and promoted their use. Some of the groups criticized guidelines on opioid prescribing issued in 2016 by the Centers for Disease Control and Prevention and attempted to limit accountability for overprescribing by lobbying against laws. They also minimized the risk of addiction.

That alignment of medicine and industry “may have played a significant role in creating the necessary conditions for the U.S. opioids epidemic, ” McCaskill’s report said.

According to the report, five manufacturers — Purdue Pharma, Janssen Pharmaceuticals, Depomed, Insys Therapeutics and Mylan — gave the money to more than a dozen groups focused on pain. Purdue, which manufactures OxyContin, gave about half the contributions, including more than $1 million to the Academy of Integrative Pain Management and more than $700,000 to the American Academy of Pain Medicine.

Purdue, in a statement, said it has supported third-party organizations “that are interested in helping patients receive appropriate care and share our commitment toward addressing the opioid crisis.”

Bob Twillman, executive director of the Academy of Integrative Pain Management, said his organization has tried to improve access to non-opioid pain relief while ensuring that patients who desperately need narcotics are able to obtain them. The American Academy of Pain Medicine said its policies do not allow “our education and advocacy positions to be compromised by outside influences.”

Insys, whose founder was charged with a “nationwide conspiracy” to illegally distribute the powerful painkiller fentanyl, gave $2.5 million to the U.S. Pain Foundation. Both said the donation was made to a fund for cancer patients.

The report’s authors say it probably reveals only a fraction of the money opioid manufacturers have spent to lobby on behalf of their products.

In statements, Depomed said it believes it acted responsibly, while Janssen said it stopped developing and promoting opioid products in 2015. Mylan said that it has cooperated with McCaskill’s investigation and that the company has played a “minuscule” role in manufacturing and marketing opioids.