The concept that likes should cure likes dates back to the Hippocrates, the Father of Medicine, who lived in the 5th century BC. It was know by Paracelsus, a Swiss physician of the 16th century. But it was Samuel Hahnemann, a German physician born in 1775, who formalized this concept into a scientific system of medicine which survives today. His first edition of the Organon, the basic book on the subject of homeopathy was published in 1810.

Dissatisfied with the medical practices of his day, Dr. Hahnemann had given up the practice of medicine and turned to translation of books to support his family. In translating Cullen's Meteria Medica , he found what he believed to be a fanciful discussion of the way that Peruvian bark, Cinchona, worked in intermittent fever. He experimented on himself by taking the substance. He found that he developed the symptoms of intermittent fever. He then used the substance to treat successfully a woman with the symptoms of relapsing fever. Cinchona was the first of many substances which Hahnemann introduced into homeopathic medicine.

Each of the remedies used in homeopathic medicine is tested in the same way that Cinchona was tested. A particular substance is administrated to a group of healthy volunteers while another group takes placebo. No one knows until after the test who took what. Careful records are kept as to the symptoms developed by the volunteers. These records provide a basis upon which a picture of that particular remedy is formed. In homeopathic treatment, the doctor matches the picture of that remedy to the picture shown by an ill person. Likes cure likes. This testing of a remedy is called "proving". Hahnemann found that, despite his use of medicines which had pictures to match the pictures of the sick person, he had trouble with the adverse effects on administrating the drugs to patients. This led him to the concept of potentization of the remedies. By this process, which consists of serial dilutions of a medicine with agitations of the solution at each step in dilution, he reduced the physical dose of medicine, while raising its energy level. Such potentized medicine he found to be very beneficial to the patient, while avoiding side effects of the crude drug.