The allegations were made on the opening day of a landmark federal trial in Oakland, California, which is expected to last six to eight weeks. The jury is expected to hear evidence from Meta chief executive Mark Zuckerberg, Instagram head Adam Mosseri and former employee and whistleblower Arturo Béjar, as well as examining internal company documents.

California deputy attorney general Megan O’Neill told jurors that Meta’s own research showed it was aware of the risks associated with Instagram. She cited a 2019 survey and internal documents which stated: “Teens are hooked despite how it makes them feel. Instagram is addictive.”

“They knew,” O’Neill said. “Time and again, profits won. If you aren’t paying for the product, you are the product. Kids are a product, and Meta took their data and used it.”

The 233-page lawsuit, filed in October 2023, alleges that Meta deliberately designed Facebook and Instagram to be addictive and continued using features it knew could harm young people.

The states also accuse the company of collecting data from children under 13 without parental consent, in breach of federal and state laws.

The case is being led by California, Colorado, Kentucky and New Jersey on behalf of the 29 states involved. The attorneys general say damages could reach $200bn (£173bn) if Meta is found liable, while also seeking changes to the design of its platforms.

Meta denies the allegations. A spokesperson said: “Rather than sticking to the facts or the law, the states have instead decided to chase an outlandish payout.

“The state AGs may call this a landmark case, but their limited claims are unsubstantiated and their financial demands are vastly disproportionate. The AGs offer no proof anyone in their states was misled, claim benign features like having an additional Instagram account somehow harmed their residents, and attempt to penalise Meta for industry-wide challenges like age verification.”

The states allege Meta developed “psychologically manipulative” features, including infinite scrolling, notifications, likes and image filters, to keep users on its platforms for longer.

Internal research is expected to include a survey of 2,500 teenagers conducted in 2019, which found: “Young people are acutely aware that Instagram can be bad for their mental health, yet are compelled to spend time on the app for fear of missing out on cultural and social trends.”

The trial comes two weeks after Meta was ordered to pay $567m to New Mexico in a separate case. Families, schools and state attorneys general have brought thousands of cases against Meta and other social media companies, drawing comparisons with litigation against tobacco firms over the health effects and addictive qualities of cigarettes.