AMNA NAWAZ: Welcome to the "News Hour."

Meta CEO Mark Zuckerberg took the stand in a Los Angeles federal court today to defend his company and its platform Instagram against allegations it was deliberately designed to be addictive to children and teens.

It's the first time he's testified about child safety in front of a jury.

The trial focuses on a now 20-year-old woman known by her initials, KGM, who says she became addicted to social media as a young girl and that excessive use exacerbated her depression, anxiety and suicidal thoughts.

GEOFF BENNETT: At issue is whether tech companies, despite knowing it would cause psychological harm, intentionally design their social media platforms to hook young users with addictive features like infinite scroll, personally tailored algorithms and push notifications.

YouTube is also included in the lawsuit.

TikTok and Snapchat chose to settle before the trial started.

The outcome will have big implications for some 1,600 similar cases across the country and could lead to monetary damages or force major changes to the platforms themselves.

For more we're joined now by NPR tech correspondent Bobby Allyn.

Bobby, it's always good to see you.

So what is the central legal question in this case and what stands out about the strategy the plaintiffs are pursuing here?

BOBBY ALLYN, Business and Technology Reporter, NPR: The central question is, are these tech companies legally culpable for hooking young people to social media apps?

And what that essentially will mean is, will they have to pay billions of dollars in monetary damages?

Will they have to make sweeping reforms to Instagram, to YouTube?

And what did they know about the harms to young people?

What did they do to conceal it to the public?

And, very importantly, Geoff, was this deliberate?

GEOFF BENNETT: As Amna mentioned, the Meta CEO,Mark Zuckerberg, he testified under oath.

What was the atmosphere in the courtroom?

You were there.

And what did he say?

BOBBY ALLYN: Yes, so Zuckerberg took the witness stand.

And you could tell he was getting kind of testy.

He often responded by saying things like, "I think you're mischaracterizing me," or "That's not what I said at all," or "I think you're taking this document out of context."

Zuckerberg was trying vociferously to demonstrate that the lawyers in the case were basically trying to lawyer him, right, to try to catch him in a gotcha moment.

But, meanwhile, what the plaintiff's lawyers were really focused on was trying to really illustrate that Zuckerberg himself was interested in recruiting and retaining children as young as 11 years old to Facebook and Instagram and keeping them on the platform for as long as possible with all of these very sticky features like likes and push notifications and beauty filters, was something that Zuckerberg himself ordered.

GEOFF BENNETT: Well, how challenging will it be for the plaintiffs to prove that these platforms were intentionally addictive?

BOBBY ALLYN: It's going to be a really uphill battle, because it's one thing that social media apps have fueled people's feelings of depression, body dysmorphia, suicide ideation, all of these other mental health issues, right, to sort of exacerbate that.

It's another to cause it.

And what experts say is adolescent mental health issues have a lot of sort of very complex root causes.

And this case is going to hinge on what degree the jury believes the companies themselves caused the mental distress that so many of these young people have experienced.

And we have one person here who's now in her 20s who says she got addicted to TikTok and Instagram and YouTube very young, but there are 1,600 other plaintiffs who have consolidated into this giant legal case against these tech giants.

So the verdict here from this jury is going to have a really, really far-reaching impact on all of these other cases that are awaiting the outcome.

GEOFF BENNETT: In the 30 seconds we have left, Bobby, for decades, as you all know, tech companies have relied on Section 230.

It's this federal law that shields these platforms from liability for user-generated content.

How does that play into all of this?

BOBBY ALLYN: Exactly.

So people say social media addiction, isn't that kind of an old issue?

We have been debating that for decades.

The reason why we haven't had a big trial until now is because of Section 230, which is a sort of impenetrable fortress for Silicon Valley.

Any time you try to sue Meta or Google or TikTok, they invoke Section 230.

The lawsuit goes away.

What's novel here, Geoff, is the legal approach.

They are attacking Meta and Google by saying this is a defective product, similar to how tobacco was a defective product.

In the '90s, there was a huge landmark lawsuit saying that they specifically targeted and misled young people to get addicted to their product.

That is what is being compared in this case, that this is the big tobacco comparison, but in the social media era.

GEOFF BENNETT: Bobby Allyn, thanks for sharing your reporting and insights with us.

BOBBY ALLYN: Thank you, Geoff.