This paper aims to critically appraise the incorporation of opium poppy into medical practice in Song-dynasty China. By analysing materia medica and formularies, along with non-medical sources from the Song period, this study sheds light on the role of Chinese Buddhist monasteries in the process of incorporation of foreign plants into Chinese medicine. It argues that Buddhist monasteries played a significant role in the evolution of the use of opium poppy in Song dynasty medicine. This is because the consumption practices in Buddhist monasteries inspired substantial changes in the medical application of the flower during the Southern Song dynasty. While, at the beginning of Song dynasty, court scholars incorporated opium poppy into official materia medica in order to treat disorders such as huangdan and xiaoke, as well as cinnabar poisoning, this study of the later Song medical treatises shows how opium poppy was repurposed to treat symptoms such as diarrhoea, coughing and spasms. Such a shift in the medical use of the poppy occurred after Chinese literati and doctors became acquainted with the role of the flower in the diet and medical practices of Buddhist monks across China. Therefore, the case study of the medical application of opium poppy during the Song dynasty provides us with insights into how the spread of certain practices in Buddhist monasteries might have contributed to the change in both professional medical practices and daily-life healthcare in local communities in that period.