For years, the U.S. Centers for Disease Control and Prevention recommended two controversial treatments for ME/CFS, the illness often known as chronic fatigue syndrome: a program of steadily increasing activity, and a specific form of cognitive behavior therapy. In early July, the agency removed information about the two treatments from the main section about the illness on its website — a move hailed by patients and advocates who had long fought for the change.

“It’s really, really significant,” said Mary Dimmock, a former pharmaceutical scientist and business analyst who turned to advocacy after her son became severely ill. The CDC’s recommendations influence medical treatment not only in the U.S. but around the world, noted Dimmock.

British psychiatrists and other experts developed the two therapies decades ago. According to their theory, these patients suffer from severe deconditioning and a misconception that they are medically sick; to get better they need to increase their levels of activity. An influential study called the PACE trial, the largest ever for the illness, reported from 2011 onwards that patients improved and could even recover from the two treatments.

But patients and advocates have long argued that the science is deeply flawed and that too much exertion can be harmful, as reported in an Undark investigation last fall. In particular, the PACE trial has come under intense international criticism for data manipulation and other serious methodological lapses.

About a million Americans are believed to suffer from ME/CFS. It most often appears to be triggered by a viral illness, or possibly other infections or environmental exposures. A 2015 report from the U.S. Institute of Medicine (now the National Academy of Medicine) concluded that it was a highly debilitating organic disease, not a psychiatric one. The distinguishing feature, the report found, was what it called “exertion intolerance” — in other words, patients suffer sustained physiological relapses after minimal amounts of physical or mental exertion. Other common symptoms include cognitive dysfunction, sleep disorders, and muscle pain.

If exertion intolerance is the distinguishing symptom, then a steady increase in physical activity — the intervention called “graded exercise therapy” promoted by PACE and included in the former CDC guidelines — would likely be considered contraindicated. In multiple surveys, many more patients have reported getting worse rather than better from graded exercise therapy. The form of cognitive behavior therapy used in PACE could also be contraindicated, since it too was designed to boost patients’ activity levels — in this instance by helping them overcome their purportedly “unhelpful” beliefs about having a medical disease.

The CDC website now advises patients to develop an individual management strategy with a health care provider and warns them not to overexert themselves. (However, a separate page about ME/CFS in the CDC’s features section still includes advice about “graded exercise.”) Yet Dimmock and other critics remain concerned that, among other problems, the website still offers little information about severely disabled patients.

In an email sent in response to questions about the changes, the CDC did not specifically mention graded exercise therapy and cognitive behavior therapy, or concerns about the PACE trial, but said that it rewrote the website section to avoid “confusion” associated with its previous recommendations and to eliminate medical jargon.

“We continue to believe that exercise can be useful for some ME/CFS patients, and also are trying to emphasize that people need to be careful not to overdo it and push themselves so far that it harms their health,” the emailed statement reads. “We also state that talking to a therapist to help find strategies to cope with their illness may be helpful. We know from our past discussions with patients and their loved ones that there has been confusion about what we recommend related to exercise and therapy. We hope that the updated website provides more clarity.”

The CDC also promised to disseminate information about the website changes once the agency has updated the companion pages for health professionals.

NOTE: The author of this post has played an advocacy role in working with physicians and patient groups to challenge the efficacy of graded exercise and cognitive behavior therapies for the treatment of chronic fatigue syndrome.

David Tuller is a lecturer in public health and journalism at the University of California, Berkeley.