In 1790 Samuel Hahnemann discovered the principle of “like curing like”. Whilst translating a book by William Cullen, Hahnemann saw that Dr. Cullen attributed the efficacy of Peruvian bark (Cinchona) in treating malaria to its bitter and astringent properties. Hahnemann disputed this point asserting that Cinchona must cure for reasons other than its bitterness and astringency, since there were many other herbs equally bitter and astringent. He decided to experiment and began to dose himself with the herb until symptoms were produced. The symptoms produced were very similar to those of Malaria. His conclusion was that the drug might be effective in treating malaria because it could cause similar symptoms in a healthy person.
It was this startling idea that led him to experiment further. Using himself, his family, and colleagues as subjects, he tested all sorts of substances. He found that any substance of plant, mineral or animal origin, given to a healthy person in repeated doses, will cause that person to develop symptoms. The same substance (in different dosage and form) will cure a sick person with a similar set of symptoms. This principle is a foundational aspect of Homeopathy and embodied in the saying: “Like may be cured by like.”
Eventually Hahnemann began to treat people basing his prescriptions on this principle of treating “like with like”. He would elicit from his patients all their symptoms and then choose a remedy which had produced symptoms that closely matched the symptoms of the illness. From the outset his results were outstanding.