Eleven people have been indicted on charges they conspired to sell counterfeit bottles of 5-hour energy drinks, says the U.S. District Attorney's office for Northern California.

Indictments against the 11 were unsealed on Thursday.

Federal prosecutors say the defendants re-labeled legitimate bottles of 5-Hour Energy drinks bound for Mexico, and they mixed counterfeit drinks in vats, flooding U.S. markets with millions of fake drinks.

The alleged conspiracy occurred between the years 2009 and 2012. The counterfeit drinks were removed from stores in 2012.

The investigation targeted defendants in California and in Mexico.

The highly caffeinated drinks are purchased by 9 million people every week with sales of $1 billion a year, a spokesman for 5-Hour Energy said.