Meta CEO and billionaire Facebook founder Mark Zuckerberg is set to be questioned for the ‌first time in a U.S. court on Wednesday about Instagram’s effect on the mental health of young users, as a landmark trial over youth social media addiction continues.

While Zuckerberg has previously testified on the subject before Congress, the stakes are higher at ​the jury trial in Los Angeles. Meta may have ​to pay damages if it loses the case, and the verdict could erode Big Tech’s long-standing legal defence against claims of user harm.

The lawsuit and others like ​it are part of a global backlash against social media platforms over children’s ⁠mental health.

Australia and Spain ⁠have prohibited access to social media platforms for users under 16, and other countries are considering similar curbs. In the U.S., Florida has prohibited companies from allowing users under 14. Tech industry trade groups are challenging the law in court.

Who is the woman behind the case?

The case involves a California woman who started using Meta’s Instagram and ⁠Google’s YouTube as a child. She alleges the companies sought to profit by hooking kids on their services despite knowing social media could harm their mental health. She alleges the apps fuelled her depression and ‌suicidal thoughts and is seeking to hold the companies liable.

Meta and Google have denied the allegations, and pointed to their work to add features that keep users safe. Meta has often pointed to a National Academies of Sciences finding that research does not show social media ​changes kids’ mental health.

The lawsuit serves as a test case for similar claims in a larger group of cases against Meta, ⁠Alphabet’s Google, Snap and TikTok. Families, school districts and states have filed thousands of lawsuits in the ⁠U.S. accusing the companies of fuelling a youth mental health crisis.

What is Meta’s defence?

Zuckerberg is expected to be questioned ⁠on ⁠Meta’s internal studies and discussions of how ​Instagram use affects younger users.

Adam Mosseri, head of Instagram, testified last week that he was unaware of a ​recent Meta study showing no ⁠link between parental supervision and teens’ attentiveness over their own social media use. Teens with difficult life circumstances more often said they used Instagram habitually or unintentionally, according to the document shown at trial.

Meta’s lawyer told jurors at the trial that the woman’s health records show her issues stem from a troubled childhood, and that ⁠social media was a creative ‌outlet for her.