The Department of Justice unsealed a civil complaint against CVS Pharmacy, alleging that for more than a decade it filled "unlawful" prescriptions for "dangerous and excessive quantities of opioids" in violation of the federal Controlled Substances Act.

The civil complaint said the largest pharmacy chain in the United States also sought reimbursement from federal healthcare programs in violation of the False Claims Act, the DOJ said in a release on Wednesday.

"CVS routinely dispensed controlled substances pursuant to prescriptions that were not valid, were not for a medically accepted indication, were not medically necessary, and/or were not issued in the usual course of professional practice," the complaint says.

"These included illegitimate prescriptions for extremely high doses and excessive quantities of potent opioids that fed dependence and addiction, as well as illegitimate prescriptions for dangerous combinations of opioids and other drugs," it went on.

The DOJ said CVS, which operates more than 9,000 pharmacies and fills more than a billion prescriptions annually, "contributed to the opioid crisis, a national public health emergency with devastating effects in the United States."

Among the prescriptions filled by CVS beginning in October 2013 were those for "dangerous and excessive quantities of opioids" and "trinity" prescriptions that included "dangerous and abused combinations of drugs" made up of an opioid, a benzodiazepine and a muscle relaxant.

CVS is also accused of filling prescriptions for drugs written by prescribers known to engage in "pill mill practices," prescribers who issue large numbers of controlled substance prescriptions without any medical purpose, the release said.

The complaint said the company ignored "substantial evidence" from external and internal sources, including its own pharmacists, that the stores were dispensing unlawful prescriptions.

"Instead of ensuring compliance with its and its pharmacists' responsibility to dispense opioids safely and legally, CVS implemented performance metrics and incentive compensation policies that it knew pressured and incentivized pharmacists to fill prescriptions as quickly as possible, without assessing their legitimacy," the complaint says.

CVS said it is cooperating with federal investigators.

"We will defend ourselves vigorously against this misguided federal lawsuit, which follows on the heels of years of litigation over these issues by state and local governments — claims that already have been largely resolved by a global agreement with the participating state Attorneys General," Amy Thibault, director of external communications for CVS, said in a written statement, the Associated Press reported.