If found liable, Walgreens, which is one of the country's largest pharmacy chains with over 8,000 pharmacies across the U.S., could face civil penalties of up to $80,850 for each unlawful prescription, the Justice Department said in a statement.

The Department of Justice sued pharmacy giant Walgreens for allegedly dispensing millions of unlawful prescriptions. Walgreens from August 2012 until the present "knowingly" filled those prescriptions, which "lacked a legitimate medical purpose, were not valid, and/or were not issued in the usual course of professional practice," the DOJ said.

The U.S. Department of Justice has filed a lawsuit against Walgreens Boots Alliance (NASDAQ:WBA) in Illinois federal court for dispensing millions of unlawful prescriptions over a 12-year period, driving Walgreens (NASDAQ:WBA) shares sharply lower in after-hours trading.