Why homoeopathic physicians prescribe only one medicine and that too in a single dose?

The concept of disease in homoeopathy is that disease is a total affection of mind and body, the disturbance of the whole organism. The parts of the body do not independently get sick. It is the whole person who gets sick. Individual organs are not the cause of illness but disturbance at the inner level (disturbance of the life force/ vital force/energy of the body) is the cause of illness. It is the whole person who is affected by the disease and it is the whole person who responds to the medicine. Therefore homoeopathy does not believe in giving different medicines for different afflicted parts of body (head, nose, ears, throat, etc ) but rather give one single constitutional remedy, which will cover the disturbance (different complaints) of the whole (same) person.