Homeopathy (also spelled homśopathy or homoeopathy) from the Greek words hómoios (similar) and páthos (suffering), is a method of alternative medicine that attempts to treat "like with like." The term "homeopathy" was coined by the German physician Christian Friedrich Samuel Hahnemann (1755–1843) and first appeared in print in 1807, although he began outlining his beliefs of medical similars in a series of articles and monographs in 1796.

Homeopathy attempts to treat the sick with extremely diluted agents that, in undiluted doses, produce similar symptoms in the healthy. However, processes used cause the dose to be exactly zero in most cases, meaning there is not a single active molecule present in the solution. Its adherents and practitioners assert that the therapeutic potency of a remedy can be increased by serial dilution of the drug, combined with succussion, or vigorous shaking. Homeopathy regards diseases as morbid derangements of the organism, and states that instances of disease in different people differ fundamentally. Homeopathy views a sick person as having a dynamic disturbance in a hypothetical "vital force", a disturbance which, homeopaths claim, underlies standard medical diagnoses of named diseases.

Evidence that homeopathy has more efficacy than a placebo is equivocal. The theory that extreme dilution makes drugs more powerful by enhancing their "spirit-like medicinal powers" is inconsistent with the laws of chemistry and physics and the observed dose-response relationships of conventional drugs; critics of homeopathy frequently describe it as pseudoscience and quackery. Placebo-controlled clinical trials have given mixed results, but most have methodological problems, with better-quality trials (e.g. those more likely to use double-blind techniques) giving negative results. Several examples of publications in high ranking journals, that are later withdrawn, are known. Additionally, cases have been reported of life-threatening complications resulting from attempts to treat serious conditions solely with homeopathic remedies.