Breast cancer patients need less anaesthetic during operations if they have been relaxed by hypnosis beforehand, US research suggests.
Breast cancer surgery patients often suffer severe side-effects
Patients in the study of 200 women by the Mount Sinai School of Medicine also reported less pain afterwards.
Breast cancer surgery patients often suffer severe side-effects such as pain, nausea and fatigue during and after their operations.
UK experts said more research was needed to prove hypnosis worked.
The side-effects from breast cancer surgery can sometimes mean a longer stay in hospital, extra drugs, or even a return to a hospital ward when patients should be recovering at home.
The Journal of the National Cancer Institute paper is just the latest to conclude hypnosis can help with operations.
Dr Guy Montgomery, who led the research, recruited 200 women to receive either 15 minutes of hypnosis or just a conversation with a psychologist before their surgery.
The women undergoing hypnosis were given suggestions for relaxation and pleasant mental images, and instructions on how to use hypnosis themselves.
Patients who had received hypnosis needed less anaesthetic than the others, and reported less pain, nausea, fatigue and emotional distress after the operation.
The researchers said this was not just better for the patients, but it added up to cash savings for the hospital, as operations took less time on the hypnotised patients, and less was spent on medication and readmission of patients.
Dr David Spiegel, from Stanford University School of Medicine, wrote in the journal: "You have to pay attention to pain for it to hurt, and it is entirely possible to substantially alter pain perception during surgical procedures by inducing hypnotic relaxation, transforming perception in parts of the body, or directing attention elsewhere.
"The key concept is that this psychological procedure actually changes pain experience as much as many analgesic medications and far more than placebos."
Dr Sarah Cant, from Breakthrough Breast Cancer, said: "This is an interesting study and anything that can help reduce the side-effects of breast surgery for breast cancer patients is to be welcomed.
"However, further, larger studies are needed before we can come to any firm conclusions about the benefits of hypnosis prior to breast surgery.
"Anyone interested in using hypnosis should discuss this with their breast care team first and ensure that they are using an appropriately trained and experienced hypnotherapist."