This study contributes to understanding medicalization on social media, by using Conrad's concept of medicalization as a theoretical framework to explore the conversation about Orthorexia Nervosa (ON) on Twitter. The aim of this mixed-methods study was twofold: the quantitative component aimed to provide descriptive information on the type of tweets and users, as well as on the network structure of the ON-related conversation on Twitter, while the qualitative component aimed to explore how the medicalization of ON unfolds on Twitter by performing a thematic analysis of original tweets about ON. Quantitative descriptive findings show that the most popular hashtags associated with orthorexia include #rdchat, #psychology and #doctors, which hints to a link between discourses around ON and the medical profession. Among the most active, prominent and visible users are news accounts, a registered dietitian, a researcher, a professor and an editor. Qualitative thematic analysis shed light on the discursive process of medicalization. Some users bring about medicalization by approaching ON as a medical entity; in contrast, other users resist medicalization by describing ON as a social phenomenon. A discursive struggle emerges, where certain individuals feel confused around what constitutes ON. This leads to stigmatization of non-traditional diets like veganism, which in turn triggers complaints regarding over-medicalization. As the first Twitter investigation on ON, this study serves the purpose of providing insights into how an emerging disorder develops in society in a time of social media.