Los Angeles, California - Instagram CEO Adam Mosseri on Wednesday rejected the notion that users could be clinically addicted to social media, as he testified in a landmark California trial over whether his company knowingly hooked children on its platform for profit.

Meta – the parent company of Instagram and Facebook – and Google-owned YouTube are defendants in the blockbuster trial, which could set a legal precedent regarding whether social media giants deliberately designed their platforms to be addictive to children.

"I think it's important to differentiate between clinical addiction and problematic use," Mosseri said as he was grilled by plaintiff attorney Mark Lanier.

"I'm sure I said that I've been addicted to a Netflix show when I binged it really late one night, but I don't think it's the same thing as clinical addiction," he added.

Lanier immediately challenged this point, emphasizing that the witness did not have a degree in medicine or psychology.

"I've never claimed being able to diagnose addiction clinically," Mosseri responded during the exchange. "I'm sure I was using the word too casually."

Facing him, mothers of teenagers who had taken their own lives held back their anger in the public gallery.

These representatives of families who have filed complaints against major platforms in the US had camped out in the rain outside the courthouse to secure seats.

Addiction is at the heart of the civil trial, which centers on allegations that a 20-year-old woman, identified as Kaley G.M., suffered severe mental harm after becoming addicted to social media as a young child.

She started using YouTube at six and joined Instagram at 11, before moving on to Snapchat and TikTok two or three years later.

"The Instagram that Kaley signed up for was very different and presented a much smaller set of risks back then," Mosseri said, noting that the service was "a much smaller, more focused app" before it had to adapt to the changing world.

Mosseri described safety features added to Instagram since it was bought by Facebook in 2012, some of which had "negative effects" on engagement and revenue.

Mosseri was the first major Silicon Valley figure to appear before the jury to defend himself against accusations that Instagram functions as little more than a dopamine "slot machine" for vulnerable young people.

Meta's attorney reasoned in opening remarks that the suffering encountered by the plaintiff was due to troubles in her home life and could not be attributed to use of Instagram or other social media.

An attorney for YouTube insisted that the video platform was neither intentionally addictive nor technically social media, but more a viewing venue like Netflix.

In front of the jury of six men and six women, Mosseri pushed back against the idea that Meta was motivated by a "move fast and break things" ethos that valued profit over safety.

"Protecting minors over the long run is even good for the business and for profit," he said.

Mosseri's testimony precedes the highly anticipated appearance of his boss, Meta founder Mark Zuckerberg, currently scheduled for February 18, with YouTube CEO Neil Mohan the following day.

In opening remarks this week, plaintiffs' attorney Lanier told the jury that YouTube and Meta both engineer addiction in young people's brains to gain users and profits.

Meta and Google "don't only build apps; they build traps," Lanier said.

Under questioning, Mosseri said that while teens tended to be trendsetters when it comes to technology, Instagram makes less money from them than from older users because they tend not to click on ads.

"They don't have a lot of expendable income to then buy things if they do click on ads," Mosseri added.

Social media firms face more than a thousand lawsuits accusing them of leading young users to become addicted to content and suffer from depression, eating disorders, psychiatric hospitalization, and even suicide.

Kaley G.M.'s case is being treated as a bellwether proceeding with an outcome that could set the tone for a wave of similar litigation across the US.

If you or someone you know needs help, please contact the 24-hour National Suicide Prevention Hotline by calling or texting 988 for free and confidential support. You can also text "HOME" to 741741 anytime for the Crisis Text Line and access to live, trained crisis counselors.