the suicide rate, especially among adolescent women has increased by almost 70% from 2001 to now, self-harm has increased, rate of depression, anxiety and related illnesses has increased in that demographic. Among young men as well, albeit to a lesser extent.
While it will take more time to figure out precisely how social media impacts the development of teenagers and young adults, the relationship is pretty unambiguous. I recommend Jonathan Haidt's latest book for anyone who still thinks that there is no very real physical and mental health threat associated with social media.