A homeopathic remedy is first tested on healthy individuals. The combined physical, emotional, mental symptoms produced by one remedy in healthy individuals are then matched to the totality of the sick individual's symptoms.
The following is a simple example of the homeopathic principle of "like cures like." Allium cepa is the Latin name for onion and when administered homeopathically to healthy individuals, it produces sniffling and watery eyes—just as a raw onion does. But when homeopathic allium cepa is given to a sick individual suffering from an allergy characterized by sniffling and watery eyes, the remedy will cure the allergy.
Remedies are made by homeopathic pharmacies from plants, minerals, animals or even allopathic drugs such as penicillin. However, unlike allopathic drugs, they are diluted to such a degree that most doses are non-material. They are sold over-the-counter in many health food stores and some pharmacies and are FDA approved.
For a more in-depth discussion of all aspects of homeopathy, see Lawrence Galante's book "Energy Medicine." For information on homeopathic credentials and how to choose a homeopath, see the National Center for Homeopathy (http://www.homeopathic.org/).