The 20-year-old woman identified as K.G.M. filed the lawsuit against Facebook and Instagram parent company Meta Platforms and Alphabet’s Google, which owns YouTube. She says the attention-grabbing design of the platforms got her addicted ⁠to them at a young age, according to court filings.

K.G.M. alleges the apps fuelled her depression and suicidal thoughts and she is seeking to hold the companies liable. A verdict against the tech companies could smooth the way for similar cases in state court and shake the industry’s long-standing US legal defence against claims of user harm. Google, Meta, TikTok and Snap face thousands of lawsuits in ‍California.

Meta Platforms CEO Mark Zuckerberg is expected to be called as a witness at the trial, which is likely to stretch ‍into March. TikTok and Snap settled with K.G.M. before the trial.

The woman’s lawyers aim to show that the companies were negligent in their design of the apps, that they failed to warn the public ‌about the risks, and that the platforms were a substantial factor in her injuries. If they succeed, the jury will consider whether to ‍award her damages for pain and suffering, and could also impose punitive damages.

Meta and Google plan to defend themselves from the claims by pointing to other factors in K.G.M.’s life, laying out their work on youth safety and trying to distance themselves from users who upload harmful content.