Meta CEO Mark Zuckerberg testified Wednesday in Los Angeles Superior Court as part of a landmark civil lawsuit accusing social media companies of deliberately designing addictive platforms that harm teen mental health. The case, known as JCCP 5255, centers on a 20-year-old woman identified as K.G.M., who alleges her social media use beginning at age 10 led to anxiety, depression, self-harm, and body dysmorphia.

During Wednesday's hearing, Zuckerberg faced questions about internal documents showing 4 million users under 13 on Instagram in 2015 and a 2015 email about increasing user engagement. The lawsuit, initially filed in 2023, includes Meta, Google's YouTube, and previously Snap and TikTok, though the latter two have settled. The case focuses on platform design rather than content, making it distinct from typical Section 230 protections.

Industry experts warn the outcome could have massive implications for social media companies. If Meta and Google lose, they could face thousands of similar lawsuits from users, school districts, and states nationwide. Columbia Law School professor Eric Talley noted that an adverse ruling would create precedent that could be "weaponized again and again" in future cases, while a win wouldn't necessarily protect the companies from ongoing litigation.