This study describes US-based physicians' online public communication practices, particularly on the social media platform Twitter/X, during the COVID-19 pandemic. We draw on 28 semi-structured interviews to examine how they responded to the unique COVID-19 context with respect to each of the four features of post-normal science (PNS): facts uncertain, values in dispute, stakes high, and decisions urgent. Our analysis reveals that the pandemic shifted what, why, and how physicians used the platform, and with whom they aimed to communicate. We discuss the implications of these changes in their online communication habits, discourses, and representations around social media as a reaction to the context of PNS brought about by the pandemic.