According to research published last month in the peer-reviewed journal "Behavioural Brain Research," Facebook may have a very real impact in the reward-related area of the brain.
Here's a quick rundown from PsyPost.org:
The researchers found that participants who opened the Facebook app more frequently and those who stayed on Facebook longer tended to have reduced gray matter volume in the nucleus accumbens.
Maybe a good reason to log on a bit less???