Reports demonstrating modest but significant correlations between heavy social media use (SMU) and poorer mental health in youth have led many to suggest that heavy SMU is culpable. Although many youth may not be harmed by heavy SMU, distressed youth may be particularly vulnerable. The aim of this study was to experimentally examine the effects of reducing SMU on smartphones on symptoms of depression, anxiety, fear of missing out (FoMO), and sleep in youth with emotional distress. A randomized controlled trial was used to assign 220 youth aged 17-25 years to either an intervention or control group. The intervention group was asked to reduce smartphone-based SMU to 1 hr/day for 3 weeks while the control group had no SMU restrictions. SMU was objectively measured daily via tracking systems in smartphones. Mental health and sleep were subjectively assessed at baseline and following the 3-week intervention period. Compared to the control group, the intervention group showed significantly greater reductions in symptoms of depression, anxiety, and FoMO, and greater increases in sleep. No effects of gender were detected. Reducing SMU on smartphones to approximately 1 hr/day may be a feasible, inexpensive, and effective method of increasing sleep and reducing symptoms of depression, anxiety, and FoMO among distressed youth. Public Policy Relevance Statement<br /> A brief 4-week intervention using screen time trackers showed that reducing social media use among heavy social media users reporting symptoms of depression or anxiety yielded significant reductions in symptoms of depression, anxiety, and fear of missing out, and increased hours of sleep relative to a comparable control group. Reducing social media use may be a feasible method of reducing distress among a vulnerable population of heavy social media users.