The first-ever jury trial over the potential harms of social media wrapped up on Thursday. Lawyers for Meta and YouTube have argued their platforms are safe for the vast majority of young people, while lawyers for a young woman at the center of the case say the tech companies have designed their products to be addictive, leading to mental health issues in children and teens.

The six-week trial has seen a parade of high-profile witnesses, including Meta chief executive Mark Zuckerberg, Instagram head Adam Mosseri and YouTube’s vice-president of engineering Cristos Goodrow. Jurors have also heard testimony from the lead plaintiff, a 20-year-old woman who goes by the initials KGM, her therapist and expert witnesses on social media and addiction.

If jurors rule in favor of KGM, the social media companies could face harsh financial penalties, which plaintiffs’ lawyers hope will lead them to change fundamental aspects of how their platforms function. In this case, the burden of proof is on the plaintiffs. The jury would need to find negligence and causation by YouTube and Meta before it could impose damages, so the outcome of the trial could take several different forms. Deliberations are set to begin on Friday.

KGM said she got hooked on YouTube starting at six and Instagram at nine. By the time she was 10, she said, she had become depressed and was engaging in self-harm as a result. The cycle of social media use caused her to have strained relationships with her family and in school, she testified. She said she had suicidal thoughts and began cutting herself as a “coping mechanism to deal with my depression”. When she was 13, KGM’s therapist diagnosed her with body dysmorphic disorder and social phobia, which KGM attributes to her use of Instagram and YouTube.

KGM’s lawyers say her experience is emblematic of what tens of thousands of young people have faced on social media and in their offline lives.

Meta and YouTube deny wrongdoing. A YouTube spokesperson, José Castañeda, called the allegations in the lawsuits “simply not true” and said that providing young people with a “safer, healthier experience has always been core to our work”.

A Meta spokesperson said in a statement that KGM’s mental health issues were brought on by a difficult home life, a key argument in the company’s case, saying she “has faced profound challenges, and we continue to recognize all she has endured. The jury’s only task, however, is to decide if those struggles would have existed without Instagram.”

This trial is the first in a consolidated group of cases brought against Meta, TikTok, YouTube and Snap on behalf of more than 1,600 plaintiffs, including more than 350 families and 250 school districts. KGM’s case was also the first of more than 20 “bellwether” trials, which are slated to go to court over the next couple of years and are used to gauge juries’ reactions as well as set legal precedent. TikTok and Snap settled the KGM case just before trial.

Online safety advocates, parents and the plaintiff lawyers say no matter how the jury decides they have already won.

“Four years ago, when we started suing social media companies, nobody thought that we would ever get to this point,” said Matthew Bergman, founder of the Social Media Victims Law Center and an attorney representing the plaintiffs. “Win or lose the outcome of this trial, victims in the United States have won, because now we know that social media companies can and will be held accountable before a fair and impartial jury.”

What was revealed during trial

KGM’s lawyers allege that some of the features that social media companies built into their platforms, such as an infinitely scrollable feed and video autoplay, are designed to keep people on the apps and create to their addictive quality. The lawyers also allege that “like” buttons feed into teens’ desire for validation and features such as beauty filters can distort young peoples’ self-image.

Troves of previously sealed documents came to light during KGM’s trial that showed some employees inside Instagram and YouTube considered the platforms either addictive or ineffective in their efforts to to protect the wellbeing of young people.

An internal document from YouTube in 2021 poses the question, “How are we measuring wellbeing?” and adds the response, “We’re not”. Another document details how kids under 13 are the fastest growing internet audience in the world and presents the opportunity of YouTube playing the digital babysitter to children as young as eight. One document reads: “[The] goal is not viewership, it’s viewer addiction.”

Documents from Meta show that some employees questioned the company’s leadership over targeting of young audiences. In an email from 2017, an employee writes to a colleague, “oh good, we’re going after <13 year olds now?”

The colleague responds, “zuck has been talking about that for a while,” which prompts the first employee to say, “yeah it was gross the last time he mentioned it”.

A separate email conversation between Meta employees in 2020 shows one person saying, “oh my gosh yall IG is a drug”. A colleague responds, “Lol, I mean, all social media. We’re basically pushers.”

The dialog continues with the employees likening social media’s draw to being similar to gambling with “reward tolerance” getting so high that people “can’t feel reward anymore”. The conversation concludes with an employee saying: “It’s kind of scary.”

During the trial, Meta and YouTube’s lawyers denied that their platforms were addictive. YouTube’s counsel pointed to parental controls and internal statistics that showed the average person’s use of the video streaming platform usually lasts less than 30 minutes a day.

Meta focused its arguments on KGM and testimony from her therapist, saying her problems had little to do with social media. Lawyers said KGM’s mother fat-shamed and screamed at her, alleging verbal abuse led to the young woman’s mental health issues. KGM still lives with her mother, who was present throughout the trial.

“Her records show significant emotional and physical abuse, academic struggles and psychiatric conditions, separate from her social media usage,” said a Meta spokesperson. “The evidence simply doesn’t support reducing a lifetime of hardship to a single factor, and our case will continue to underscore that reality.”

Meta also contended with the idea of addiction, saying that KGM never received that official diagnosis. When Mosseri took the stand, he took it further by pushing back on the science behind social media addiction, denying that users could be “clinically addicted”. Psychologists do not classify social media addiction as an official diagnosis, but researchers have documented the harmful consequences of compulsive use among young people.

KGM’s lawyers’ arguments mirror those brought against big tobacco in the 1990s, which focused on cigarettes’ addictive qualities and companies publicly denying that for decades even while knowing their products’ harms. Online safety advocates and parents say Meta has refused to look at its effect on young people and instead used a “blame the victim” tactic.

“They’re really truly pulling from big tobacco’s playbook. Blame the victim, blame the parents, blame the child, blame anyone but the products they designed,” said Sacha Haworth, the executive director of the Tech Oversight Project, which has been involved in advocacy work for the plaintiffs.

“These are the most profitable corporations in the history of the world. And they could make these changes if they wanted to. But instead of doing that, they attack the victims.”