Kim, Kourtney and Khloe Kardashian have been hit with a $5 million lawsuit.

The sisters are among those named in a class action suit filed in Manhattan, New York by a group of disgruntled customers, who claim diet pills QuickTrim, which are endorsed by the 'Keeping up with the Kardashians' stars, don't live up to their weight-loss claims.

According to the New York Post, the lawsuit reads: "In reality, QuickTrim's main ingredient is a large dose of caffeine, which the FDA [Food and Drug Administration] has determined is not a safe or effective treatment for weight control."

The group claim they would have not bought the products if they were aware of this.

The federal court filing adds that QuickTrim is "marketed by the defendants as a clinically proven formula that will increase metabolism, curb appetite and promote weight loss".

The lawsuit also claims that a number of advertisements for the QuickTrim weight-loss pills feature the Kardashian sisters in "in a bikini or other revealing attire".

Kim - who has more than 13.5 million followers on social networking site twitter - tweeted last June: "Starting QuickTrim today. It's officially summer. I want to really get in fab shape! Whose with me? (sic)"