This study examined the relationship between social media usage patterns and mental health outcomes among students at Kyambogo University in Uganda. Using a mixed-methods research design, the study collected data from 384 undergraduate students through structured questionnaires incorporating validated psychological assessment tools, focus group discussions, and in-depth interviews. The research found that 77.1% of students engaged with social media platforms for three or more hours daily, with WhatsApp (97.1%), Facebook (82.3%), and TikTok (70.6%) being the most widely used platforms. Concerning mental health indicators were observed, including moderate to severe anxiety symptoms in 39.9% of respondents, depressive symptoms in 33.6%, and poor sleep quality in 62.2% of the student population. Significant correlations were established between daily social media usage time and all measured mental health variables, with particularly strong relationships observed with sleep disturbances (r=0.531, p<0.001) and social media addiction tendencies (r=0.682, p<0.001). The nature of engagement significantly influenced psychological outcomes, with passive consumption consistently associated with poorer mental health compared to active content creation and meaningful interaction. Multiple regression analyses identified social comparison tendencies (β=0.329) and fear of missing out (β=0.243) as critical mediating variables explaining how platform engagement translated into psychological distress. The study also revealed that strong offline social support served as a significant buffer against negative mental health outcomes (β=-0.284, p<0.001), and digital literacy skills demonstrated significant moderating effects on the relationship between social media usage and anxiety (p<0.01). Background of the study. The proliferation of social media platforms over the past decade has fundamentally transformed how university students communicate, socialize, and access information. Platforms such as Facebook, Instagram, Twitter,