According to the lawsuit, the Labor Department issued the advisory opinion after Morgan Stanley launched an extensive campaign with its law firm.

"By tackling branded pharmas and equitable pricing strategies that have left Americans carrying the financial weight of global drug innovation, the government is helping to relieve a long-standing burden on U.S. consumers and businesses," David Joyner, the CVS chief executive officer, said.

The study compared changes in the Consumer Price Index (CPI) across 23 major metropolitan statistical areas (MSAs) to provide a snapshot of short- and long-term inflation trends.