Kim and Khloe Kardashian have been hawking diet product QuickTrim for a while now, but it may not actually work—or be safe. A law firm representing one unhappy QuickTrim user is reaching out to others, and is reportedly prepping a class action lawsuit against the Kardashians, the New York Post reports. The firm's website claims that QuickTrim's active ingredient is "a large dose of caffeine," which "the FDA has determined … is not safe or effective for weight loss." A physician also warned against QuickTrim in 2010, cautioning that it could actually lead to caffeine poisoning. (More QuickTrim stories.)