The current study aims to examine the relationship between Social Media Use Disorder (SMUD) and Orthorexia Nervosa (ON), and evaluate the indirect effect of loneliness in this association. This cross-sectional study was carried out between July and September 2021. A total of 363 university students were recruited through convenience sampling through several universities in Lebanon’s governorates. Data about information about the social media applications mostly used (Instagram, Facebook, Twitter, etc.), the number of times of entry to social media applications, the time spent on these applications, ON, loneliness and SMUD, were also collected. The Mplus v.7.2 software was used to estimate categorical confirmatory factor analyses (CFA) of the SMD and loneliness scales. The one-factorial model of the SMD scale fitted well according to χ2/df (69.71/27 = 2.58), TLI (.967), CFI (.956), and RMSEA values (.066; CI [.047–.085]; pclose = .079). The one-factorial model of the loneliness scale fitted well according to χ2/df (10.30/5 = 2.06) TLI (=0.97), CFI (=0.98), and RMSEA values (=0.054; CI [0.000–0.101]; pclose = 0.379). When entering the social media applications and time spent on these applications as independent variables in a first regression model, using Instagram (Beta = 2.73), using Tumblr (Beta = 3.22), spending 30–60 minutes per day on social media apps compared to less than 30 minutes (Beta = 2.33), higher physical activity index (Beta = 0.04) and loneliness (Beta = 0.67) were significantly associated with more ON. When entering the SMUD score as an independent variable in a second regression model, the results showed that higher SMUD (Beta = 0.50) was significantly associated with more ON. Also, loneliness played a partial indirect role in the association between SMUD and ON (by 16%). The current results can help mental health professionals better detect these potential psychological disorders and might help improve future treatment of issues related to ON and SMUD.