LOS ANGELES, United States (AFP) — A landmark social media trial began in earnest on Monday that could establish a legal precedent on whether Meta or YouTube deliberately designed their platforms to lead to addiction in children.

Rival attorneys were set to make their case to a Los Angeles jury in a trial that is expected to see Meta chief Mark Zuckerberg on the stand next week and Instagram boss Adam Mosseri in the courtroom as early as Wednesday.

The trial is being keenly watched because it could establish a legal precedent on whether social media companies deliberately designed their platforms to hook children too vulnerable to look away.

The case is being seen as a bellwether proceeding because its outcome could set the tone for a tidal wave of similar litigation across the United States.

Defendants at the trial are Alphabet and Meta, the tech giants behind YouTube and Instagram.

Neil Mohan, the head of YouTube, is also expected to be called.

Social media firms are accused in hundreds of lawsuits of leading young users to become addicted to content that has led to depression, eating disorders, psychiatric hospitalisation and even suicide.

Lawyers for the plaintiffs are borrowing strategies used in the 1990s and 2000s against the tobacco industry, which faced a similar onslaught of lawsuits arguing that companies sold a harmful product.

On Friday, lawyers for the defence unsuccessfully sought to bar plaintiffs from comparing their platforms to tobacco and other addictive products.

The trial before Judge Carolyn Kuhl focuses on allegations that a 20-year-old woman identified by the initials K.G.M. suffered severe mental harm because she became addicted to social media as a child.

“This is the first time that a social media company has ever had to face a jury for harming kids,” Social Media Victims Law Center founder Matthew Bergman, whose team is involved in more than 1,000 such cases, told AFP.

The centre is a legal organisation dedicated to holding social media companies accountable for harm allegedly caused to young people online.

Internet titans have argued that they are shielded by Section 230 of the US Communications Decency Act, which frees them of responsibility for what social media users post.

However, this case argues that those firms are culpable for business models designed to hold people’s attention and to promote content that can harm their mental health.

“The allegations in these complaints are simply not true,” said Jose Castaneda, a YouTube spokesperson.

“Providing young people with a safer, healthier experience has always been core to our work,” he added.

Meta has also rejected the allegations.

Snapchat and TikTok were named as defendants in the suit, but struck settlement deals before the start of the trial. The terms were not disclosed.

Lawsuits, including some brought by school districts, accusing social media platforms of practices endangering young users are making their way through federal court in northern California and state courts across the country.

A separate lawsuit accusing Meta of putting profit over the wellbeing of young users is also getting under way in New Mexico.

“Our investigation into Meta’s social media platforms demonstrates that they are not safe spaces for children but rather prime locations for predators to trade child pornography and solicit minors for sex,” New Mexico Attorney General Raul Torrez said in a statement.

Meta has rejected the accusations and vowed to defend itself in court.

Jury selection in the Los Angeles case ended on Friday, with Meta dismissing several jurors over their strong opinions about either social media in general or Zuckerberg specifically.