Yes, research demonstrates a significant effect when using hypnosis for weight loss. In a 9-week study of two weight management groups (one using hypnosis and one not using hypnosis), the hypnosis group continued to get results in the two-year follow-up, while the non-hypnosis group showed no further results (Journal of Clinical Psychology, 1985).
In a study of 60 women separated into hypnosis versus non-hypnosis groups, the groups using hypnosis lost an average of 17 pounds, while the non-hypnosis group lost an average of only .5 pounds (Journal of Consulting and Clinical Psychology, 1986).
In a meta-analysis, comparing the results of adding hypnosis to weight loss treatment across multiple studies showed that adding hypnosis increased weight loss by an average of 97% during treatment, and even more importantly increased the effectiveness POST TREATMENT by over 146%. This shows that hypnosis works even better over time (Journal of Consulting and Clinical Psychology, 1996)