Homeopathy or homoeopathy is a pseudoscientific. system of alternative medicine. It was created in 1796 by Samuel Hahnemann. Its practitioners, called homeopaths, believe that a substance that causes symptoms of a disease in healthy people would cure similar symptoms in sick people; this doctrine is called similia similibus curentur, or “like cures like”. Homeopathic preparations are termed remedies and are made using homeopathic dilution. In this process, a chosen substance is repeatedly and thoroughly diluted. The final product is chemically indistinguishable from the diluent, which is usually either distilled water, ethanol or sugar; often, not even a single molecule of the original substance can be expected to remain in the product. Between the dilution iterations homeopaths practice hitting and/or violently shaking the product, and claim that it makes the diluent remember the original substance after its removal. Practitioners claim that such preparations, upon oral intake, can treat or cure disease.

All relevant scientific knowledge about physics, chemistry, biochemistry and biology gained since at least the mid-19th century confirms that homeopathic remedies have no active content. They are biochemically inert, and have no effect on any known disease. Hahnemann’s theory of disease, centered around principles he termed miasms, is inconsistent with subsequent identification of viruses and bacteria as causes of disease. Clinical trials have been conducted, and generally demonstrated no objective effect from homeopathic preparations. The fundamental implausibility of homeopathy as well as a lack of demonstrable effectiveness has led to it being characterized within the scientific and medical communities as quackery and nonsense.