Relation to evidence-based medicine

Some scientists reject the use of the classification of any therapy as 'alternative medicine' on the grounds that "[t]here is only medicine that has been adequately tested and medicine that has not, medicine that works and medicine that may or may not work." These scientists advocate a classification based on scientific evidence, and claim that "[w]hat most sets alternative medicine apart, in our view, is that it has not been scientifically tested and its advocates largely deny the need for such testing." The US Institute of Medicine analyzed this approach to defining alternative medicine, which it called normative, and found it problematic because some CAM is tested, and much of mainstream medicine lacks strong evidence. The IOM noted that in study of 160 Cochrane systematic reviews of mainstream techniques, 20% were ineffective and 21% had insufficient evidence. The IOM therefore defined alternative medicine broadly as the nondominant approach in a given culture and historical period. A similar definition has been adopted by the Cochrane Collaboration, which is the leading body of evidence-based medicine, and official government bodies such as the UK Department of Health.

Well-known proponents of evidence-based medicine, such as the Cochrane Collaboration and Edzard Ernst, Professor of Complementary Medicine at the University of Exeter, use the term alternative medicine but agree that all treatments, whether "mainstream" or "alternative", ought to be held to standards of the scientific method. Their view is that evidence-based medicine is an ideal state which has not yet been achieved by either current mainstream or alternative medicine. Ernst characterizes the evidence for many alternative techniques as weak, nonexistent, or negative, but notes that compelling evidence exists for others, particularly certain herbs and acupuncture – although this evidence does not mean these treatments are mainstream, especially not worldwide. What is alternative varies by discipline as well and country. For example, biofeedback is commonly used within the Physical Medicine & Rehabilitation community, but is considered alternative within the medical community as a whole, and some herbal therapies are mainstream in Europe, but are alternative in the United States.

Criticisms of CAM by mainstream physicians have been numerous. Barrie R. Cassileth has succinctly summed up the situation:

"Not all mainstream physicians are pleased with CAM, with current efforts to integrate CAM into mainstream medicine, or with a separate NIH research entity for "alternative" medicine. Vigorous opposition to CAM as "pseudo science" based on "absurd beliefs" continues to be voiced. CAM's deviation from basic scientific principles, implicit, for example, in homeopathy and therapeutic touch, are decried. A 1997 letter to the US Senate Subcommittee on Public Health and Safety signed by four Nobel Laureates and other prominent scientists deplored the lack of critical thinking and scientific rigor in OAM-supported research."

According to the NCCAM, formerly unproven remedies may be incorporated into conventional medicine if they are shown to be safe and effective. Several scientists share this point of view and state that "[o]nce a treatment has been tested rigorously, it no longer matters whether it was considered alternative at the outset. If it is found to be reasonably safe and effective, it will be accepted." According to them it is possible for a method to change categories (proven vs. unproven) in either direction, based on increased knowledge of its effectiveness or lack thereof. Prominent proponents of this position are George D. Lundberg, former editor of the Journal of the American Medical Association (JAMA), and Phil B. Fontanarosa, Senior Editor of JAMA," Richard Dawkins, Professor of the Public Understanding of Science at Oxford, and Stephen Barrett, founder and operator of Quackwatch, who argues that techniques currently labeled "alternative" should be reclassified as "genuine, experimental, or questionable. Genuine alternatives are comparable methods that have met science-based criteria for safety and effectiveness. Experimental alternatives are unproven but have a plausible rationale and are undergoing responsible investigation. ... Questionable alternatives are groundless and lack a scientifically plausible rationale. ... Blurring these distinctions enables promoters of quackery to argue that because some practices labeled "alternative" have merit, the rest deserve equal consideration and respect. Enough is known, however, to conclude that most questionable "alternatives" are worthless. Oxford University Press publishes a peer-reviewed journal entitled Evidence-based Complementary and Alternative Medicine (eCAM).

M.R. Tonelli argues that CAM cannot be evidence-based unless the definition of evidence is changed. He states that "the methods of developing knowledge within CAM currently have limitations and are subject to bias and varied interpretation. CAM must develop and defend a rational and coherent method for assessing causality and efficacy, though not necessarily one based on the results of controlled clinical trials." Further, A review of Michael L. Millenson's book Demanding Medical Excellence: Doctors and Accountability in the Information Age described it as "a wake up call to both medicine and nursing" due to what Millenson calls a "lack of scientific-based medical practice". According to the review, the book states that "85% of current practice has not been scientifically validated" and that it suggests that users of the research presented by Medline should question research articles rather than assuming they are accurate simply because of where they are published. The review states that Millenson's thesis and conclusion call for all health researchers and policy makers do a better job in assuring valid methodology and avoidance of bias in published research. Michael Dixon, the Director of the NHS Alliance stated that “People argue against complementary therapies on the basis of a lack of evidence. But I’d say only 10 per cent of what doctors do in primary care is evidence-based." Angell and Kassirer acknowledge that "many treatments used in conventional medicine have not been rigorously tested, either" but note that the scientific community is generally aware that this is a failing that needs to be remedied."

Many CAM methods are criticized by the activist non-profit organization Quackwatch.