Many of the therapies housed under the rubric of CAM are not new in the United States. In the 19th century and into the early years of the 20th century, practices that we would now consider alternative flourished. Some of these therapies have persisted, and some, such as osteopathy and chiropractic, have even been legitimized by the courts. However, the present practice of these two modalities barely resembles their common roots in bone setting. Other therapies – nostrums and secret potions, exorcism, and mesmerism – fell out of favor long ago. The same is true of medicine. Certain centuries-old methods of diagnosis and treatment used by medical professionals have also experienced lasting value, whereas others have not withstood the test of time. Physicians still examine a patient's temperature to ascertain the presence of infection. They no longer, however, subject patients to bloodletting, purging with calomel, or dosing with strychnine (the latter for post surgery patients), to name a few.

Despite these similarities, the course of alternative medicine and its place in American health care diverged widely from that of conventional medicine as the 20th century progressed. In becoming alternative, these practices also became ostracized. They were no longer part of “regular” medicine because their practitioners were not trained as physicians and their practices were not based on science, which had gradually come to inform the practice of medicine. As the status of medicine advanced, alternative practices seemed to disappear.