Hypnosis has been used for thousands of years to help overcome difficulties, boost optimism and positive attitude and even to help physical ailments such as high blood pressure, warts, verrucas and pain. Hypnosis works because the capacity to go into trance and change state is an essential human faculty (although in fact trance behavior can be observed in animals too).
Because hypnosis is a naturally occurring human experience (unlike medication, with its side-effects) it can be entirely good for a person and, used well, is entirely safe.
You can learn more about hypnosis here.
There have been hundreds of research studies documenting the beneficial power of hypnosis. See our comprehensive articles on hypnosis.