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 medicine" is a loosely defined and very diverse set of products, practices, and theories that are perceived by its users to have the healing effects of medicine, but do not originate from evidence gathered using the scientific method, "Biomedicine" is that part of medical science that applies principles of anatomy, physics, chemistry, biology, physiology, and other natural sciences to clinical practice, using scientific methods to establish the effectiveness of that practice.
Much of what is now categorized as alternative medicine was developed as independent, complete medical systems, was developed long before biomedicine and use of scientific methods, and was developed in relatively isolated regions of the world where there was little or no medical contact with pre-scientific western medicine, or with each other's systems.
Practices such as chiropractic and osteopathic, each considered to be irregular by the medical establishment, also opposed each other, both rhetorically and politically with licensing legislation.
Homeopathy was developed prior to discovery of the basic principles of chemistry, which proved homeopathic remedies contained nothing but water.
But homeopathy, with its remedies made of water, was harmless compared to the unscientific and dangerous orthodox western medicine practiced at that time, which included use of toxins and draining of blood, often resulting in permanent disfigurement or death.
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.