Hypnosis is completely safe because you are in control at all times. For something to pass into the subconscious you always control it from your values and beliefs. Therefore there is no chance of something going against the principles of the individual.
Hypnosis has been approved by the British Medical Association in 1955 and the American Medical Association in 1958. The American Psychological Association has approved hypnosis as a science in 1960. Even before official recognition, for over 200 years, doctors and psychologists have been using hypnosis as a therapeutic method.