Social networking sites such as Facebook and Twitter feed anxiety and make people feel inadequate, a study has found.
A poll of those using the technology found more than half of those surveyed said the sites had changed their behaviour - and half of those said their lives had been altered for the worse.
Most commonly, those who suffered a negative impact from social media said their confidence fell after comparing their own achievements to those of friends online.
Two-thirds said they found it hard to relax completely or to sleep after spending time on the sites.
And one quarter of those polled said they had been left facing difficulties in their relationships or workplace after becoming confrontational online.