Reiki has been a part of my treatments for many years. I use this technique only when I feel the patient is fully comfortable with receiving this type of approach, or asks for it himself.
I am a strong believer that the body has the capacity to heal itself, but it is undeniable that we often need an external force to help us with that process.
There is no exact study that has been done that can prove that Reiki, on its own, can cure any disease or injury.
But we cannot deny that our mind, and our body are connected, and that one over time can affect the other. In many cases, these problems result in a "disturbed" energy flow in the body. Reiki is an alternative method, that often calms the mind and relaxes the body. When stress levels decrease, physical tensions decrease, and the mind starts to calm down. It is then that the body starts letting go of the well known "fight and flight" modus, and makes space for the body to heal itself.
It is valuable to realize that the therapist is just helping the patient to achieve this goal, not the therapist who is healing the patient with his hands.
It is for that reason that Reiki can possibly help for any type of Physical or Mental distress.