During the Covid-19 pandemic, many users consider Twitter as a reliable source of medical information, which is often distorted unintentionally while shared. Through the qualitative study of 106 tweets about controversial treatments, we show that despite the information quality in the initial tweet, the public figures' feeds evoke cascades contributing to misinformation circulation. We clarified the mechanism of the medical information distortion within cascades, discovered the main actors in the discussion on the controversial medical treatment, and showed group polarisation effect. Oversimplification of the medical issue allows lay users to conform controversial and unclear prescriptions of different doctors to the very clear political opposition.