Similia similibus curentur (Like cures like)

Hahnemann recognized that many natural products produce pharmacological or toxicological effects, which he refers to as symptoms.  He believed that substances that produce symptoms similar to a given disease should be used to treat that disease.   He states:

The curative power of medicines, therefore, depends on their symptoms, similar to the disease but superior to it in strength (§12-26), so that each individual case of disease is most surely, radically, rapidly and permanently annihilated and removed only by a medicine capable of producing (in the human system) in the most similar and complete manner the totality of its symptoms, which at the same time are stronger than the disease.  (Organon, sixth edition).

He felt that the artificially induced disease (caused by the medicine) would push aside the pathologic disturbance in the vital force and replace it with this new, pharmacologically-induced disturbance in the vital force.  The body could then overcome this artificial disturbance and a cure would be effected.  In Hahnemann's words:

As every disease ...  consists only in a special, morbid, dynamic alteration of our vital energy (of the principle of life) manifested in sensation and motion, so in every homoeopathic cure this principle of life dynamically altered by natural disease is seized through the administration of medicinal potency selected exactly according to symptom-similarity by a somewhat stronger, similar artificial disease-manifestation. By this the feeling of the natural (weaker) dynamic disease-manifestation ceases and disappears. This disease-manifestation no longer exists for the principle of life which is now occupied and governed merely by the stronger, artificial disease-manifestation. This artificial disease-manifestation has soon spent its force and leaves the patient free from disease, cured. The dynamis, thus freed, can now continue to carry life on in health.