People with a positive frame of mind about back pain, who are in control of their condition, experience less back-related disability during the course of treatment.

"The analysis showed that psychological factors were consistently associated with back-related disability," explained Felicity Bishop from the University of Southampton and arthritis research UK career development fellow.

"People who started out with very low expectations of acupuncture who thought it probably would not help them were more likely to report less benefit as treatment went on," Bishop noted.

Acupuncture is one of the most established forms of complementary therapy which is recommended in clinical guidelines.

For the study Bishop recruited 485 people who were being treated by acupuncturists, and they completed questionnaires before they started treatment, then two weeks, three months and six months later.

The questionnaires measured psychological factors, clinical and demographic characteristics and back-related disability.

"This study emphasizes the influence of the placebo effect on pain. The process whereby the brain's processing of different emotions in relation to their treatment can influence outcome is a really important area for research," concluded Stephen Simpson, director of research at Arthritis Research UK.

The findings were published in The Journal of Clinical Pain.

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