Two US senators have sent a letter to TikTok executives demanding answers about an experiment the company ran that withheld a safety feature from millions of users — including a teenager who died by suicide. The lawmakers, co-sponsors of an online child safety bill, called TikTok’s decision to conduct the test “depraved.”

The existence of the experiment, described in detail in a confidential 2023 company document, was reported by Bloomberg Businessweek this month. The disclosure prompted the letter sent Wednesday by Republican Senator Marsha Blackburn of Tennessee and Connecticut Democrat Richard Blumenthal to TikTok Inc. Chief Executive Officer Shou Chew and to Adam Presser, CEO of the company’s US spinoff.

“We write regarding disgusting new reports that TikTok knowingly withheld a critical safety measure for millions of American users — including children — in order to determine whether protecting users would impact its financial bottom-line,” the four-page letter began. The Businessweek story’s “appalling” revelations, the senators wrote, “raise serious questions about TikTok’s repeated assurances to Congress, parents and the American public that it prioritizes the safety and well-being of young people over profit.”

The TikTok document — handed over in litigation against the world’s biggest social media companies and placed under a court-ordered seal — shows the company intentionally switched off an algorithmic safeguard for 10% of US users, turning them into a control group. The safeguard was designed to break up online echo chambers of harmful content. At the time, that control group amounted to approximately 15 million people. Randomly withholding a feature from a slice of users — a control group — is a standard method tech platforms use to measure whether changes move core metrics. The practice has drawn scrutiny in this case because the withheld feature was a safety safeguard rather than a design tweak, and because the affected pool included minors.

One of them was 16-year-old Chase Nasca of Bayport, New York. According to the document, his account was fed thousands of videos about sadness, hopelessness, loneliness and suicide right up until he killed himself. Chase was randomly selected for the algorithm experiment on Jan. 25, 2022. Within a month, he was dead.

The document explains why his account received what it called an “onslaught” of dark content: “TikTok’s filter bubble prevention strategies did not take effect on this user by design.” It also states the company’s rationale for turning off the safety setting for some users: “The user impact decision was a delicate balance across safety and the ability to measure impact on DAU (daily active users) and core metrics.”

TikTok did not respond to a request for comment about the letter. In a statement provided for the Businessweek story, however, a TikTok spokesperson said the company was “deeply committed to the safety and well-being of users,” especially teens. “Our hearts break for any family that experienced a tragic loss,” the spokesperson said. “To help protect our community, we continue to invest significantly in Trust & Safety, including robust detection systems and dedicated enforcement teams that proactively remove content that violates our Community Guidelines.”

In their letter, Blumenthal and Blackburn noted that Congress had raised concerns about TikTok’s algorithm driving young users toward harmful content since October 2021 — before the company rolled out the experiment. The revelations, the senators wrote, “are made even more sinister because TikTok was on notice about the effects of its recommendation algorithms on children.”

The senators demanded answers to 13 questions, including the names of every employee informed of the experiment; an explanation of why the company permitted minors to be included in the test; details on when executives learned about the experiment; and a “complete, unredacted version” of the document reported by Businessweek. They also asked for a list of every algorithmic experiment in the US in which TikTok has “withheld, disabled, delayed, or reduced a safety feature,” along with the number of users involved and how many of them were minors. The senators gave the company until Sept. 1 to respond. The deadline sets the timeline for what, if anything, the company discloses from a document that remains under court-ordered seal.

“The fact that they did this knowingly and that they used their users as an experiment is something that just seems inconceivable,” Blackburn said in an interview conducted after the Businessweek story was published but before the letter was sent. “It shows you how when our children are on these social media platforms — they are the products.”

To Blackburn, the experiment is a clear example of a company prioritizing “making money and capturing eyeballs” over safety. “Look at the fact that this was a happy, 16-year-old boy with no mental health issues and then, over this short window of time, the impact of feeding video after video after video and post after post after post about depression and suicide and what it did to this child. It is frightening — and this is something that these platforms need to be held to account for,” she said.

Florida Republican Representative Gus Bilirakis echoed Blackburn’s concerns in a written statement, saying the report was deeply troubling and demonstrated the “devastating consequences that can occur when engagement metrics and corporate profits are prioritized over the safety and well-being of our children.” During a hearing in March 2023, weeks after the confidential document was created, Bilirakis had questioned TikTok CEO Chew about Chase Nasca and told him, “Your technology is literally leading to death.” Chew responded that the company takes these issues “very seriously” and provides mental health resources to users who search for suicide content.

Bilirakis and Blackburn both said American families have waited too long for protections for children online and called for child safety bills to be fast-tracked. Blackburn is pushing the Kids Online Safety Act (KOSA), a Senate bill she co-authored with Blumenthal to force tech platforms to prioritize child safety above profits. The bill died in the House in 2024 but was reintroduced this legislative session. Bilirakis championed the Kids Internet and Digital Safety (KIDS) Act, which includes most of the Senate bill as well as laws covering AI chatbots and video games. It passed the House in June.

The House bill stripped a so-called duty-of-care provision from the Senate’s version, which would have forced tech companies to exercise reasonable care to prevent mental health harms to minors — including anxiety, depression and compulsive usage of social media products. The provision was removed over First Amendment concerns. Because legislation must clear both chambers in identical form, the duty-of-care provision is the principal difference lawmakers would have to resolve between the House-passed bill and the Senate version for any final child-safety law.

On Aug. 5, the day after the Businessweek story was published, the Senate Committee on Commerce, Science and Transportation voted to advance the original, revived KOSA, with the duty-of-care provision intact. That provision, Blackburn said in the interview, would help prevent future experiments like this one because social media platforms would be required to prioritize safety in the design of their products, especially for teens. Clearing committee is the step that typically precedes consideration of a bill by the full Senate.