thumb|right|250px|A homeopathic remedy prepared from marsh Labrador tea, diluted to the point where it almost certainly contains no molecules of the original herb.

Homeopathy is a form of alternative medicine that treats a disease with heavily diluted preparations that are thought to cause effects similar to the disease's symptoms. First expounded by German physician Samuel Hahnemann in 1796, homeopathic preparations are serially diluted with shaking ("succussing") after each step under the assumption that this increases the effect of the treatment. This dilution often continues until none of the original substance remains. . Since homeopathic remedies generally contain few to zero pharmacologically active ingredients, they are generally thought to have no effect beyond placebo by mainstream medical practitioners. Modern homeopaths have proposed that water has a memory that allows homeopathic preparations to work without any of the original substance; however, the physics of water is well understood, and no known mechanism permits such a memory.

Apart from the symptoms of the disease, homeopaths use aspects of the patient's physical and psychological state in recommending remedies. . Homeopathic reference books known as repertories are then consulted, and a remedy is selected based on the index of symptoms. Homeopathic remedies are generally considered safe, with rare exceptions.

However, homeopaths have been criticized for putting patients at risk with advice to avoid conventional medicine, such as vaccinations,

anti-malarial drugs, and antibiotics.

In many countries, the laws that govern the regulation and testing of conventional drugs do not apply to homeopathic remedies.

Claims of homeopathy's efficacy (beyond the placebo effect) are unsupported by the collective weight of scientific and clinical evidence.

Specific pharmacological effect with no active molecules violates fundamental principles of science,

Supporters claim that studies published in reputable journals support the efficacy of homeopathy; however, there are only a handful of them, they are not definitive and they have not been replicated.

Several high-quality studies exist showing no evidence for any effect from homeopathy, and the few positive studies of homeopathic remedies have generally been shown to have problems that prevent them from being considered unambiguous evidence for homeopathy's efficacy. The lack of convincing scientific evidence supporting homeopathy's efficacy and its use of remedies lacking active ingredients have caused homeopathy to be described as pseudoscience