Alternative medicine or fringe medicine are practices claimed to have the healing effects of medicine but which are disproven, unproven, or impossible to prove, and are possibly harmful; and where the scientific consensus is that the therapy does not, or can not, work because the known laws of nature are violated by its basic claims. Alternative therapies or diagnoses are not part of medicine or science-based healthcare systems. Alternative medicine consists of a wide variety of practices, products, and therapies—ranging from those that are biologically plausible but not well tested, to those with known harmful and toxic effects. Contrary to popular belief, significant expense is paid to test alternative medicine, including over $2.5 billion spent by the United States government. Almost none show any effect beyond that of false treatment. Perceived effects of alternative medicine may be caused by placebo; decreased effect of functional treatment (and therefore potentially decreased side effects); and regression toward the mean where improvement that would have occurred anyway is credited to alternative therapies; or any combination of the above. Alternative treatments are neither the same as experimental medicine, nor traditional medicine — although the latter, when used today may constitute alternative treatments.
Alternative medicine has grown in popularity and is used by a significant percentage of the population in many countries. While it has extensively rebranded itself: from quackery to complementary or integrative medicine—it promotes essentially the same practices. Newer proponents often suggest alternative medicine be used together with functional medical treatment, in a belief that it "complements" (improves the effect of, or mitigates the side effects of) the treatment. There is no evidence showing they do so, and significant drug interactions caused by alternative therapies may instead negatively influence treatments, making them less effective, notably cancer therapy. Despite being illegal to market alternative therapies for cancer treatment in most of the developed world, many cancer patients use them.
Alternative medical diagnoses and treatments are not taught as part of science-based curricula in medical schools, and are not used in any practice where treatment is based on scientific knowledge or proven experience. Alternative therapies are often based on religion, tradition, superstition, belief in supernatural energies, pseudoscience, errors in reasoning, propaganda, fraud, or lies. Regulation and licensing of alternative medicine and health care providers varies between and within countries.
Alternative medicine is criticized for being based on misleading statements, quackery, pseudoscience, antiscience, fraud, or poor scientific methodology. Promoting alternative medicine has been called dangerous and unethical. Testing alternative medicine that has no scientific basis has been called a waste of scarce research resources. Critics state "there is really no such thing as alternative medicine, just medicine that works and medicine that doesn't", and the problem with accepting any alternative treatment is that the "underlying logic is magical, childish or downright absurd". It has been strongly suggested that idea of any alternative treatment that works is paradoxical, as any treatment proven to work is by definition "medicine".