How do you know they work? Is it an assumption based upon your own personal experience or that of a friend or family members?
There have literally been hundreds upon hundreds of studies, most of which were controlled well and are considered to be high quality and they all indicate homeopathy has no medical value aside from a mild placebo effect. Large scale meta-analyses (analyzing many, often hundreds, of studies to try to get an overall conclusion) indicate homeopathy to have no medical value.
In addition the majority of homeopathic preparations don't even have a single molecule of "medication," it is diluted to the point it is simply water and many tests have shown that a homeopathic treatment and plain water produce the same level of results, well within placebo range.
Only a few tests indicate anything positive about homeopathy however most are low quality studies and they have not or can not be reproduced (it is a fundamental principal in science that a study must be able to be recreated). Even many of the tests preformed or recommended by homeopaths fail. In total the number of 'positive studies,' typically only showing a small possible benefit, is extremely small compared to the body of information discrediting homeopathy.
The American Medical Association and The United Kingdom National Health Service (NHS) along with countless other highly respected major medical organizations have stated that homeopathy has no medical value. Even a large number of organizations promoting complimentary and alternative medicine have publicly stated that homeopathy has no medical value.
I am a medical student at a university in Montréal, QC, Canada for psychiatry and internal medicine. I have a Hons. BSc in pharmacology and I have interned with two psychiatrists and one neurologist. In addition, I have worked as a pharmacy assistant.