Using Facebook can reduce young adults' sense of well-being and satisfaction with life, a study has found.
Checking Facebook made people feel worse about both issues, and the more they browsed, the worse they felt, the University of Michigan research said.
The study, which tracked participants for two weeks, adds to a growing body of research saying Facebook can have negative psychological consequences.
Facebook has more than a billion members and half log in daily.
"On the surface, Facebook provides an invaluable resource for fulfilling the basic human need for social connection. Rather than enhancing well-being, however, these findings suggest that Facebook may undermine it," said the researchers.
Internet psychologist Graham Jones, a member of the British Psychological Society who was not involved with the study, said: "It confirms what some other studies have found - there is a growing depth of research that suggests Facebook has negative consequences."
But he added there was plenty of research showing Facebook had positive effects on its users.
In the survey, participants answered questions about how they felt, how worried they were, how lonely they felt at that moment, and how much they had used Facebook since the last survey.
They received five text messages each day at random times between 10:00 and midnight, containing links to the surveys.
Researchers also wanted to know about how much direct interaction participants had with people - either face-to-face or by phone - between questionnaires.
Results showed that the more people used Facebook, the worse they felt afterwards. But it did not show whether people used Facebook more or less depending on how they felt, researchers said.
The team also found that the more the participants used the site, the more their life satisfaction levels declined.
The pattern appeared to contrast with interacting "directly" with people, which seemed to have no effect on well-being.
But researchers did find people spent more time on Facebook when they were feeling lonely - and not simply because they were alone at that precise moment.
"Would engaging in any solitary activity similarly predict declines in well-being? We suspect that they would not because people often derive pleasure from engaging in some solitary activities (e.g., exercising, reading)," the report said.
"Supporting this view, a number of recent studies indicate that people's perceptions of social isolation (i.e. how lonely they feel) are a more powerful determinant of well-being than objective social isolation."
Colloquially, this theory is known as FOMO - Fear Of Missing Out - a side effect of seeing friends and family sitting on beaches or having fun at parties while you are on a computer.
Learning the rules
According to the study, almost all the participants said they used Facebook to stay in touch with friends, but only 23% said they used the social networking site to meet new people.
More than three-quarters said they shared good things with their communities on the site, while 36% said they would share bad things on Facebook as well.
Mr Jones warned that the study's findings were probably most relevant to people who spent too much time on Facebook, and the study did not offer a full comparison with "direct" social contact.
He also said that since Facebook was such a recent phenomenon, society was still learning to use the platform.
"As a society as a whole we haven't really learnt the rules that make us work well with Facebook," he said, adding some people became unable to control their experience with it.
The researchers said their study was the first to examine the effect Facebook has on its users' well-being over time.