The Kardashians might be in trouble again as sisters Kim and Khloe face a possible class action lawsuit due to a product which they recently endorsed.

According to the reports, weight loss supplement QuickTrim, which Kim and Khloe have been endorsing since 2009, is non-FDA approved and allegedly contains an unsafe amount of caffeine. Bursor & Fisher, the law firm preparing the class action lawsuit against Windmill and the marketing claims made by Kim and Khloe, sent an email to QuickTrim users asking if they want to join the class action lawsuit. The email reads, “The active ingredient in QuickTrim weight loss products is a large dose of caffeine. The FDA has determined that caffeine is not safe or effective for weight loss.”

“My firm has been retained by an individual that purchased QuickTrim, and we are investigating the matter,” partner Scott A. Bursor told New York Post about the class action lawsuit they filed. “We have provided written notice of our client’s claims to the company and others involved in marketing QuickTrim.” Bursor & Fisher has won or settled cases against firms peddling products including hair loss remedy Avacor and diet supplement Xenadrine.

Adriane Fugh-Berman, a physician at Georgetown University Medical Center, warned in 2010 that QuickTrim contains large amounts of caffeine. Fugh-Berman said, “They’re not saying how much caffeine is in these pills. Too much caffeine can make you jittery and increase your blood pressure and pulse. If you pop a couple of these pills with your Starbucks, you could get caffeine poisoning, which can cause heart arrhythmia.”

The Kardashian sisters Kim and Khloe are featured in ads for QuickTrim, donning barely-there bikinis, and tweet regularly to millions of their followers about their own personal use of the weight loss supplement. Also, in January 2010, Kim said she used QuickTrim to lose 15 pounds in weeks. Last year, she also tweeted that she was using QuickTrim to get in shape for her wedding, and Khloe also claimed she lost 15 pounds.