The rising phenomenon of addictive social media use, categorized under behavioral addictions in both ICD-11 and DSM-V, is increasingly attracting scientific and therapeutic focus. This issue is particularly critical during adolescence and young adulthood—a period marked by significant developmental tasks, including the development of autonomy. Given that social media usage can influence user autonomy, it is essential to explore its broader impact on cognitive, emotional, and regulatory dimensions of autonomy. To investigate this, we conducted a study involving 108 young adults aged 18-27 in Germany, examining their social media habits alongside their autonomy levels across different dimensions. Using regression, correlation, and moderation analyses, we discovered a significant negative correlation between social media consumption and all autonomy dimensions, irrespective of gender. Notably, this relationship was mediated by the subjective experience of fear of missing out (FoMO). Our findings suggest that excessive social media use is linked to increased FoMO, which in turn, hinders autonomy development in young adults. This underscores the need for clinicians working with this demographic to closely monitor social media consumption at every stage of therapeutic intervention—from anamnesis and diagnostics to treatment and aftercare. Furthermore, these results support the recognition of social media addiction as a distinct form of technology-related behavioral addiction.