Abstract The Covid-19 pandemic has pushed medical discourse to the forefront of everyday communication, but limited scholarly attention has been given to its intersection with social-mediated language use in the Chinese context. From a corpus-pragmatic view, we examined textual data collected from Zhihu, the most popular Chinese community question-answering site. Our analysis focused on the linguistic mechanism of evidential expression in social-mediated debates on Traditional Chinese medicine (TCM). Within the realm of medical scientific discussion, we identified a prevailing epistemic stance of doubt and uncertainty towards the efficacy of TCM, emphasising its socio-political significance. We also demonstrated how the ‘source of knowledge’ value and the ‘speaker commitment’ value of evidentiality interact at the semantic-pragmatic interface. Our findings shed light on a promising research trajectory for sociolinguistic intervention in the formal, descriptive line of evidentiality research, thus, advancing existing corpus pragmatics literature on evidentiality and epistemics in social-mediated communication.