Facebook acknowledged on Friday that too much social media can be bad for you, a remarkable admission as the 2-billion member online service battles mounting criticism about its impact on society.

In a blog post published on Friday, Facebook addressed a “hard question”: “Is spending time on social media bad for us?” In it, the social networking firm cites academic research indicating that in certain instances using Facebook can have a negative effect on people’s moods, and that heavier users of the site can have worse mental health.

“Researchers hypothesize that reading about others online might lead to negative social comparison,” wrote Facebook director of researcher David Finsberg and research scientist Moira Burke, “and perhaps even more so than offline, since people’s posts are often more curated and flattering.”

Facebook also cited research showing the positive impact of social media. “In sum, our research and other academic literature suggests that it’s about how you use social media that matters when it comes to your well-being.”

The post by Facebook underscores the thorny situation facing the company, which has built a $28 billion business on an advertising model that relies on people spending as much time on its site as possible. Globally, the average user spent 50 minutes every day using Facebook’s various suite of apps, CEO Mark Zuckerberg said in April 2016.

But Facebook also counters this with evidence that engaging with others online “is linked to improvements in well-being,” and that Facebook can have other positive impacts.