For years, technology companies have insisted that social media is only one part of a far more complicated youth mental health crisis.

A California jury has now found that argument was not enough.

After nine days of deliberations, jurors found Google and Meta negligent in the design and operation of YouTube and Instagram, concluding that both companies knew, or should have known, their platforms posed a danger to minors.

The jury also found the companies failed to adequately warn users about those risks and that their negligence was a substantial factor in the harm suffered by the plaintiff.

She was awarded $US3 million, equivalent to about $4.3 million.

The case is being closely watched because it is the first of thousands of lawsuits accusing major technology companies of knowingly building products that exploit the habits and vulnerabilities of children.

Plaintiff began using platforms as a child

The 20-year-old plaintiff told the Los Angeles court she began using YouTube at six and Instagram at nine.

She says her use eventually became an “all day long” addiction that worsened her mental health.

Her lawyers argued that the platforms were not passive services, but carefully engineered products built to hold the attention of young users for as long as possible.

They pointed to endless scrolling feeds, autoplay functions, notifications and recommendation systems that continually deliver fresh content without requiring users to make a conscious decision to continue.

Those features, the plaintiff’s legal team argued, were designed to “hook” children and encourage compulsive use.

Verdict is a referendum — from a jury, to an entire industry 

“Today’s verdict is a referendum — from a jury, to an entire industry — that accountability has arrived,” the plaintiff’s counsel said in a statement.

The verdict represents a major legal setback for Google and Meta, which have repeatedly rejected claims that their platforms are responsible for individual mental health outcomes.

Throughout the trial, Meta argued that the plaintiff’s difficulties existed independently of her social media use and repeatedly pointed to instability in her home life.

Lawyers representing both companies also highlighted the parental controls, safety systems and screen-time tools available to users.

YouTube challenged claims about the amount of time the plaintiff spent on the platform, telling the court that usage records showed she averaged little more than one minute a day.

Google spokesperson Jose Castañeda said the verdict misrepresented YouTube, “which is a responsibly built streaming platform, not a social media site”.

An Australian mother who welcomed the landmark ruling said the $4.3 million penalty amounted to little more than “a slap in the face”, given the scale and financial power of Google and Meta.

She argued the companies should have been ordered to pay at least $20 million, saying a larger penalty was needed to send a genuine “shot across the bow” warning to tech companies about the consequences of platforms that contribute to social media addiction.

Meta to appeal verdict

Meta has already confirmed it will appeal.

Meta spokesperson Andy Stone said teen mental health was “profoundly complex” and could not be linked to a single app.

“We respectfully disagree with the verdict and will appeal,” he said in a statement.

“We will continue to defend ourselves vigorously as every case is different, and we remain confident in our record of protecting teens online.”

Former Meta executive says platforms are ‘addictive by design’

Former Meta engineering director and whistleblower Arturo Béjar, who appeared as a witness for the plaintiff, described the verdict as “wonderful”.

Béjar led safety and security work at Meta from 2009 to 2015 and returned to the company between 2019 and 2021.

“It’s so clear the way that these products are designed, they’re addictive by design,” he told ABC NewsRadio.

“The techniques they use inevitably will make a young person addicted to these products.

“It’s a long road ahead but I hope this is the day we’ll remember as the day the world got to see these products and these people for what they are.”

Thousands of similar cases remain pending

The verdict is expected to carry consequences well beyond the damages awarded to one plaintiff.

Thousands of related lawsuits are now moving through US courts, many alleging that social media companies knowingly created products that expose children to compulsive use, depression, eating disorders, self-harm and suicide-related content.

Laura Marquez-Garrett, a lawyer with the Social Media Victims Law Center, said the case should be viewed as the beginning of a wider legal reckoning.

“This case is historic no matter what happens because it was the first,” she said during deliberations.

“This trial was a vehicle, not an outcome.”

Snap and TikTok reached settlements with the plaintiff before the trial began, leaving Google and Meta to face the jury.

Pressure builds on technology companies

The ruling comes as American lawmakers increase pressure on technology companies over their treatment of children and teenagers.

At least 20 US states enacted laws last year dealing with children’s social media access, phone use in schools and age-verification requirements for online accounts.

The Los Angeles verdict also follows a separate finding in New Mexico this week, where a jury concluded Meta had violated state law by misleading users about the safety of Facebook, Instagram and WhatsApp and enabling child sexual exploitation across its platforms.

Together, the cases mark a significant shift in the legal battle over social media harm.

The question confronting technology companies is no longer limited to whether children are being damaged online.

Courts are now being asked to decide whether the platforms were built in ways that made that harm predictable — and whether the companies behind them should be forced to pay for it.