Homeopathy (also spelled homoeopathy or hom?opathy) is a form of alternative medicine, first proposed by German physician Samuel Hahnemann in 1796, that attempts to treat patients with heavily diluted preparations. Based on an ipse dixit axiom formulated by Hahnemann which he called the law of similars, preparations which cause certain symptoms in healthy individuals are given as the treatment for patients exhibiting similar symptoms. Homeopathic remedies (Homeopathy#Homeopathic remedies) are prepared by serial dilution with shaking by forceful striking, which homeopaths term succussion, after each dilution under the assumption that this increases the effect of the treatment. Homeopaths call this process potentization. Dilution often continues until none of the original substance remains.

Apart from the symptoms of the disease, homeopaths use aspects of the patients physical and psychological state in recommending remedies.citation author=Hahnemann S (Samuel Hahnemann)title =The Organon of the Healing Art year =1833 edition=5th at=aphorisms 5 and 217 isbn=0879832282. Homeopathic reference books known as repertories are then consulted, and a remedy is selected based on the totality of symptoms. Homeopathic remedies are, with rare exceptions, considered safe though homeopathy has been criticized for putting patients at risk due to advice against conventional medicine (Evidence-based medicine) such as vaccinations, anti-malarial drugs, and antibiotics.

Homeopathys efficacy beyond the placebo effect (placebo) is unsupported by the collective weight of scientific (scientific method) and clinical (clinical medicine) evidence.UK Parliamentary Committee Science and Technology Committee - "Evidence Check 2: Homeopathy" While some individual studies have positive results, systematic reviews of published trials fail to demonstrate efficacy conclusively. Furthermore, higher quality trials (Clinical trial) tend to report less positive results, and most positive studies have not been replicated or show methodological problems that prevent them from being considered unambiguous evidence of homeopathys efficacy. A 2010 inquiry into the evidence base for homeopathy conducted by the United Kingdoms House of Commons Science and Technology Committee (Science and Technology Select Committee) concluded that homeopathy is no more effective than placebo.

Depending on the dilution, homeopathic remedies may not contain any pharmacologically active (pharmacology) molecules, and for such remedies to have pharmacological effect (Pharmacology) would violate fundamental principles of science. Modern homeopaths have proposed that water has a memory (water memory) that allows homeopathic preparations to work without any of the original substance; however, there are no verified observations nor scientifically plausible physical mechanisms for such a phenomenon. The lack of convincing scientific evidence supporting homeopathys efficacy and its use of remedies lacking active ingredients have caused homeopathy to be described as pseudoscience, quackery, and a "cruel deception".

The regulation and prevalence of homeopathy is highly variable from country to country. There are no specific legal regulations concerning its use in some countries, while in others, licenses or degrees in conventional medicine from accredited universities are required. Some homeopathic treatment is covered by the national insurance coverage of several countries; in others it is fully integrated into the national health care system. In many countries, the laws that govern the regulation and testing of conventional drugs do not apply to homeopathic remedies.