Hypnotherapy though is effective, does not really help in people that are psychosis and of any mental disorder type.
These people can easily get triggered and enter into the conditions of mental disorder. Especially hypnosis is about by-passing the conscious mind and go direct to the subconscious, it is even more dangerous for this group of people.
The words of the hypnotherapist could be misunderstood as some negative voices trying to harm them.
As such, they are best left to psychiatrist or mental doctor for treatment. Perhaps medication is a better choice.