It's worth thinking first what "hypnosis" means.
This is not easy as experts argue about it all the time.
Certainly what often passes as hypnosis is nothing more than some sort of compliance to social norms or authority figures.
Imagine a charismatic Freud like man with a small beard and a commanding voice telling you to "go down now into a deep trance" and you might well obey him -- particularly if you had an expectation that he was going to resolve some long-standing problem that you had.
Simple compliance of this kind is not itself a trance, though it may or may not involve it.
On the other hand it I asked you to go back in your mind and remember the very first book you ever read and recall as much of it as you possibly can, page by page, word by word, then you probably would go into some sort of genuine trance.
Trance states involve focus of attention.
They also involve how you use your senses.
As you go deeper into trance conscious attention narrows and unconscious attention expands.
Now the fact is that individual parts of the brain have different ways of working.
They even encode information in different ways.
You may believe one thing at one level "I am going to succeed" and something quite different at another "The truth is I am not sure I really can do it.
" Therapeutic trance invokes these different states and at its best facilitates a more satisfactory adjustment between them.
Its purpose is not to reprogram you but rather to provide integration between different parts of you.
The effectiveness with which this happens depends on the skill of the hypnotist.
Your conscious mind may abhor some behavior triggered by your unconscious mind.
On the other hand your unconscious mind will have some kind of positively purposeful intent -- it will just not be what the conscious mind expects or desires.
Compliance to authority is what we all need to escape.
That lets other people think for you and control your actions.
Hypnosis in the therapeutic setting is potentially the reverse - a force that increases freedom to expand and become the person you really are.
In doing so it simply accelerates and encourages processes that do quite naturally occur.
Hypnosis is therefore safe for treatment.