As of 2019, just as traditional Chinese medicine, there are no established nor a generally agreed and accepted theories among the scientific community about how Homeopathy works.
The best and most reasonable theory on the action of homeopathic remedies I found is by Vithoulkas. According to George Vithoulkas in one of his lectures, homeopathic remedies have retained a sort of bio-active properties during the process of serial potentization, homeopathy is also often referred to as “energy medicine”, the idea is that an organism vibrates at a certain frequency at each moment and the remedy works by a sort of resonance of the energy between the organism and the remedy.
Symptoms are the immune system’s BEST EFFORT at getting rid of a disease, the symptoms themselves are NOT the disease. Symptoms are the best possible ways that an organism have evolved to deal with problems, and the correct remedy gives extra energy to the organism to do its own things following the natural course of defence after millions of years of evolution.
For example, nasal mucous contains the best possible cocktail of natural chemicals to trap and destroy pathogenic bacteria, in the case of common upper respiratory infection, nasal discharge is increased to promote a swift self-healing process, a prolonged nasal discharge condition only means the best effort of the organism is still not good enough, remember when you tried so hard at school and you still failed your exam?
A correct homeopathic remedy can stimulate the organism to produce more discharge and complete the natural healing process; on the contrary, an allopathic chemical designed to dry up the nose will allow the bacteria to travel further down deeper into the respiratory tract and limit the organism even more! Unfortunately, so far only the minority have dared to challenge why mucous blocker is still the usual prescription.
And by the way, this was one of the numerous oxymoron concepts that I had spent years to investigate, you may find out more from my book, ‘An Introduction to Classical Homeopathy‘.
In summary, classical homeopathy worked very well for me and my friends and is popular and regulated in many countries, how it works had remained controversial as of year 2019.