Meta quietly shut down ‘Project Mercury’: Why the company shelved a study showing quitting Facebook reduced anxiety

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Newly unsealed court documents in the United States have revealed that Meta quietly shut down an internal mental health study after early results suggested that stepping away from Facebook made users feel better.

The study, known internally as Project Mercury, began in late 2019 and was aimed at understanding how Facebook and Instagram affected users’ emotional wellbeing. The findings were never made public. Instead, the project was discontinued after results appeared to contradict Meta’s public claims about user safety.

These revelations are part of a larger lawsuit accusing major social media companies of knowingly exposing young users to mental health risks while publicly denying harm.

What Project Mercury was designed to test

Project Mercury was launched to measure how social media use shaped mood, behaviour and self-perception. Meta partnered with Nielsen to survey users who voluntarily stopped using Facebook or Instagram for periods ranging from one week to one month.

Participants were then analysed for changes in loneliness, stress, anxiety, social comparison and general emotional wellbeing.

According to the unsealed filings, users who paused Facebook use reported feeling less lonely, less anxious and less pressured by social comparison. Even a break of just seven days showed noticeable improvements in emotional state.

These results suggested that the platform itself may have been contributing to stress for some users.

Why Meta ended the project

Instead of expanding the study or publishing the results, Meta discontinued Project Mercury. The filings allege that the company cast doubt on the data and privately downplayed its significance.

Internal staff questioned this decision. One employee wrote, “The Nielsen study does show causal impact on social comparison,” highlighting concern about ignoring the findings.

Another employee raised a more serious ethical question, warning that hiding negative results could make Meta look like tobacco companies that suppressed evidence about harmful products. The message read, “If the results are bad and we don’t publish and they leak, is it going to look like tobacco companies doing research and knowing cigs were bad and then keeping that info to themselves?”

What the lawsuit claims

The wider legal case argues that Meta and other social platforms prioritised growth and engagement over user safety. It accuses the company of suppressing research that showed harm to young users while assuring lawmakers and the public that such harm could not be reliably measured.

The filings also allege that Meta designed safety systems that were ineffective or deliberately slow. One document claims that a user had to be flagged for sex trafficking behaviour 17 times before being removed, described as “a very, very, very high strike threshold.”

Other claims suggest Meta delayed stronger safety measures to avoid reducing engagement levels.

The documents further reference a 2021 exchange in which Mark Zuckerberg said he would avoid stating that protecting children online was his top focus, saying, “when I have a number of other areas I’m more focused on like building the metaverse.”

Meta’s response

Meta has rejected the allegations and defended its decision to end Project Mercury. Company spokesperson Andy Stone said the study was flawed and influenced by users who already believed Facebook was harmful to them.

He stated, “The full record will show that for over a decade, we have listened to parents, researched issues that matter most, and made real changes to protect teens.”

Stone also said, “We strongly disagree with these allegations, which rely on cherry-picked quotes and misinformed opinions.”

He added that people who felt Facebook was unhealthy naturally felt better when they stopped using it, and that this did not prove the platform directly caused harm.

Other platforms also under scrutiny

The lawsuit also names TikTok, Snap and Google’s YouTube. TikTok is accused of influencing child-focused organisations through paid partnerships, while Google has denied wrongdoing, saying, “These lawsuits fundamentally misunderstand how YouTube works and the allegations are simply not true.”

Why this matters

The legal case represents one of the most serious challenges yet to the social media industry. If the court finds that Meta suppressed harmful findings, it could force major changes in how platforms conduct and disclose internal research.

A hearing scheduled for January 26, 2026 will decide whether more internal documents remain sealed or are made public.

For critics, Project Mercury is now seen as a symbol of a wider problem. It suggests that Meta may have known its platforms were harming users but chose silence over transparency.