Mark Zuckerberg faced intense questioning in a Los Angeles courtroom as part of a major trial examining whether social media platforms intentionally addict and harm children.

Testifying on Wednesday, the Meta CEO defended his company’s policies on youth safety and Instagram use, saying existing scientific research has not conclusively proven that social media causes mental health harm. He rejected claims that the company set goals to increase user time on Instagram, although he acknowledged such metrics were used in the past before shifting focus to “utility.”

The lawsuit was filed by a 20-year-old woman, identified as KGM, who alleges early social media use worsened her depression and suicidal thoughts. Meta and Google’s YouTube remain defendants, while TikTok and Snap have settled similar claims.

During cross-examination, plaintiff lawyer Mark Lanier presented internal documents suggesting time-spent targets were previously encouraged. Zuckerberg insisted a “reasonable company” should help users, not exploit them.

He also addressed criticism over beauty filters and age verification, saying there was insufficient evidence of harm and that Meta works to block users under 13 and detect false age claims.

Children’s advocates criticised his testimony as misleading, while Meta’s lawyers argued the plaintiff’s mental health struggles stemmed from personal factors rather than Instagram.

The bellwether case could influence thousands of similar lawsuits against social media firms.