Smartphone-based social media is the principal cause of the rise in adolescent depression, anxiety, and self-harm seen across the U.S., U.K., Canada, Australia, and the Nordic countries since roughly 2012.
What makes this case stronger than a typical "X happened, then Y happened" story is that three patterns line up on the same hypothesis, and they don't easily line up on others. The timing: rates of depression, self-harm, and suicide among teens turn upward within a narrow window in the early 2010s, in countries that s…