Lead plaintiff, now 20, says use of social media made her relationships with friends and family anxious and strained

The young woman at the heart of the landmark trial about the addictive nature of social media testified for the first time on Thursday, saying she got hooked on YouTube starting at age six and Instagram at nine. By the time she was 10, she said, she had become depressed and was engaging in self-harm.

The woman, who is now 20 and known by her initials KGM, is the lead plaintiff in an expansive lawsuit against YouTube and Meta, which owns Instagram and Facebook. The crux of the case alleges social media companies intentionally create addictive products, leading to mental health issues in young people.