Physicians have extensive clinical knowledge and are thus uniquely positioned to offer public health education through social media (SM) platforms. However, it may be challenging for them to effectively communicate complex medical information to lay people with varying levels of related knowledge. There is limited research on how physicians navigate these challenges. This study uses affordance actualisation theory to investigate how a prominent physician adapts SM features to effectively disseminate medical and scientific information. The study identifies two key SM actualisation practices in this process. First, the process involves balancing knowledge brevity to improve accessibility while maintaining information fidelity to ensure accuracy. Second, the process involves providing valuable clinical insights while adhering to legal constraints in the open SM environment through the optimisation of SM features as a compensatory mechanism. The current findings contribute to a theoretical framework on how physicians manage medical knowledge flow online, which involves not only advancing knowledge but also carefully regulating knowledge to maintain accuracy and professional standards within the open nature of SM.