Althought the principles have been known since the time of Hypocrates, the idea of like curing like was not commonly used until a German physician, Samuel Hahnemann (1755-1843) came to devise the system of medicine that we know today as homeopathy.
Hahnemann trained in medicine and chemistry. Working as a doctor in the late 18th century, he was dissatisfied with the conventional medical practices of his day. Blood-letting, purging and giving patients large doses of toxic materials such as arsenic and lead were commonplace. Hahnemann disagreed with these harsh methods.
He was investigating the effects of various medicinal substances on himself and other healthy volunteers when he deduced that an illness could be treated with a very small amount of a substance that, in larger quantities, could cause that illness.
To avoid harmful effects from normal doses of the substances he diluted each medicine until he reached the greatest dilution that would still produce a response. These experiments were called provings and led him to observe and describe the basic principles of homeopathic medicine.