Homeopathy rests on two linked ideas set out by Samuel Hahnemann. The first, similia similibus curentur, or like cures like, holds that a substance capable of producing a set of symptoms in a healthy person can cure a sick person showing those same symptoms; Hahnemann arrived at the idea after taking cinchona bark, a source of quinine, and noting that it produced symptoms resembling the malaria it was used to treat. The second is potentization: homeopathic remedies are prepared by repeatedly diluting a substance, often in a ratio of one part in a hundred at each step, with vigorous shaking, or succussion, between dilutions. Many common homeopathic remedies are diluted well past the point, given by Avogadro's number, at which a dose is statistically likely to contain even a single molecule of the original substance; homeopathic theory holds that succussion imprints the substance's therapeutic pattern onto the diluting medium itself, a claim with no accepted basis in chemistry or physics.
In practice, a homeopathic consultation typically involves a detailed intake of the patient's physical and emotional symptoms, matched against a large reference literature, the materia medica, to select a single remedy believed to fit that individual's whole symptom picture rather than a named disease. Remedies are sold over the counter in many countries as well as prescribed by trained homeopaths, and the practice remains popular worldwide, particularly in parts of Europe and India, even as its proposed mechanism sits outside accepted science and its clinical trial record has not supported its specific claims.