We cannot assume that one type of medicine when taken, can definitely cure everyone with that same illness. This is a wrong thinking.
The reason is because there are a few different body types or constitutions existing. Which body type will affect how your body response to the medicine. Coupled with the other factors like your belief and mood, the medicine would turn out to be ineffective to one person but totally effective for another.
The same applies to hypnotherapy and any other type of therapeutic methods.