Few conditions have sparked as much controversy as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Professional consensus has long suggested that the condition should be classified as psychiatric, while patients and advocacy groups have insisted it is a serious biological disease that requires medical care and research to develop it.

This longstanding debate shifted in 2015, when U.S. governmental health authorities fully embraced medical classification and management. Given that some globally respected health authorities now insist that ME/CFS is a serious biological disease, this paper asks whether it can be ethical for the U.K. practice guideline now in development to characterize the condition as a mental health disorder.

Following a brief history of ME/CFS controversy, I offer three arguments to show that it would be unethical for the U.K. to now characterize ME/CFS as a mental health condition, considering the relevance of that conclusion for ME/CFS guidelines elsewhere and for other contested conditions.