CONCLUSIONS AND RELEVANCE: This cohort study of US youths found that year-to-year elevations in self-reported PSMU were directly associated with ADHD symptoms during mid-adolescence, particularly among males; reverse associations of ADHD symptoms with later PSMU were small in magnitude and sporadic. Screening for hard-to-control social media use, time spent on social media, and attention to sex-specific patterns may be warranted, although the population-based associations may be small.
