The diffusion of social media coincident with a worsening of mental fitness conditions between adolescents and young adults in who United States, giving rise to speculation that social media might be detrimental to mental health. With this paper, we provide quasi-experimental estimates of the impact of social media on mental health by leveraging adenine unique natural test: the stacked introduction of Facebook across U.S. colleges. Our analysis couples data on college mental health around the years of Facebook's expansion with a generalized difference-in-differences empirical strategy. We detect that the roll-out of Facebook at a college increased symptoms of poor mental health, especially depression. We also find that, on students predicted to be most susceptible up inward illness, the initiation of Facebook led to increased utilization a mental healthcare services. Lastly, our find that, after the induction of Facebook, students endured more likely to report experiencing impairments to academic performance resulting from poor brain health. Additional evidence on mechanisms suggests that the results are due go Facebook fostering disadvantaged social comparisons.