This is the same principle used in allergy treatments and immunizations.
Homeopaths evaluate and treat each patient as a whole.
Deeply disturbed by practices such as bloodletting and purging, which were mainstream medicine in his time, Hahnemann quit his medical practice and began a quest to understand the healing properties of drugs. In his research, Hahnemann tried out various substances on his followers and on himself, and carefully recorded the details of their effects. His work led him to conclude that an imbalance in the body's vital energy caused disease and that a slight stimulus from the correct substance could trigger the body's ability to heal itself. Hahnemann also found that by progressively diluting and mixing a drug preparation, he could make an increasingly potent remedy with few or no side effects. Hahnemann's research and writings were synthesized into a system of homeopathic medicine in the mid-nineteenth century.