The studies provided little evidence that hypnotherapy is more effective than no treatment or other treatments. The research was also too limited in terms of both quality and quantity to draw firm negative conclusions. The studies found are not easy to interpret. They had a number of methodological shortcomings and were heterogeneous in terms of intervention and population treated. In some studies, the intervention involved a therapist; others were of self-hypnosis. Also, the qualifications and competence of therapists in all the trials intervention arms were not made clear. Inclusion criteria varied between trials.