Gov. Gavin Newsom of California signed legislation on Friday aimed at protecting minors from social media addiction amid growing concerns about the impact of technology on adolescents’ mental health.

The law, which will go into effect in 2027, effectively requires tech companies to make posts on feeds of minors’ social media accounts appear in chronological order as a default, rather than allowing algorithms to curate them to maximize engagement.

The bill also prohibits companies from sending notifications to people under 18 during school hours, from 8 a.m. to 3 p.m. on weekdays from September through May, and during sleep hours, between midnight and 6 a.m. The default settings can be changed with the consent of a parent or guardian.

“Every parent knows the harm social media addiction can inflict on their children — isolation from human contact, stress and anxiety, and endless hours wasted late into the night,” Mr. Newsom, who has four school-age children, said in a statement on Friday.

The move, targeting powerful tech interests in the nation’s most populous state, is part of a nationwide effort to address concern over cellphone and social media use among adolescents. Amid reports of cyberbullying and distraction in classrooms, at least eight states, including Florida and Indiana, have already enacted restrictions on the use of cellphones in school settings. New York put in place a similar law aimed at social media addiction this year.

In June, Governor Newsom also called for a ban on smartphone use in all public schools in California. Legislation now before him includes a requirement that the schools devise a policy by July 1, 2026, to limit or prohibit smartphones during the school day, though most school districts already have cellphone policies.

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