Alternative medicine is defined as "any of various systems of healing or treating disease (as chiropractic, homeopathy, or faith healing) not included in the traditional medical curricula taught in the United States and Britain". Complementary medicine is defined as "any of the practices (as acupuncture) of alternative medicine accepted and utilized by mainstream medical practitioners". The term complementary and alternative medicine (CAM) is an umbrella term for both branches. CAM includes practices that incorporate spiritual, metaphysical, or religious underpinnings; non-evidence based practices, non-European medical traditions, or newly developed approaches to healing.

The list of therapies included under CAM changes gradually. If and when an unproven therapy is proven to be safe and effective, it becomes adopted into conventional health care and gradually ceases to be considered "alternative", since adoption and acceptance often take time. If a CAM therapy is proven dangerous and ineffective, it should cease to be advocated by CAM practitioners, although there are no clear instances of this happening.